cid
Latincut, kill
About This Root
Picture a Roman with a blade. The Latin verb caedere meant to strike with a sharp edge — to cut, to fell, to kill. Its present stem shows up as -cid- and its past-participle stem as -cis-, and English inherited both. From that single swing of the blade, two great branches grew, and the prefix tells you what the blade is doing.
The killing branch lives in the suffix -cide, which names either the act of killing or the thing that does the killing. Here the prefix names the victim: sui- (oneself) + cide = suicide; homo- (a human being, from Latin homo) + cide = homicide; geno- (a race or people) + cide = genocide; patri- (father) + cide = patricide. Modern chemistry borrowed the same machine to coin product names — pest + i + cide = pesticide, herb + i + cide = herbicide, insect + i + cide = insecticide, fungi + cide = fungicide, bacteri + cide = bactericide. In every one, -cide is the killer; the front of the word is what gets killed.
The cutting branch lives in -cise/-cis, and here the prefix tells you how the cut is made. prae- (before, in front) + cis = precise: cut off right at the front, trimmed to the exact edge — nothing extra. con- (thoroughly) + cis = concise: cut down to the essentials. in- (into) + cis = incise, incision: a cut made into a surface, as a surgeon's cut into skin; the incisor is the front tooth that cuts. ex- (out) + cis = excise, excision: to cut something out and remove it. The scissors are the two-bladed tool that cuts, and even chisel traces back through Old French to caedere — the blade that cuts stone and wood.
Between the two branches sits the most useful word of all: decide. de- (off, away) + caedere = to 'cut off' — and what you cut off are all the other choices. When you decide, you take a knife to a branching set of options and sever every path but one. That is why a decisive person is one who cuts cleanly, and why someone who is undecided is still standing at the fork with the knife unraised.
A caution: cid (caedere, cut/kill) is not the same root as cad (cadere, to fall), even though English spelling pushes them together in words like incident and coincidence. Those belong to falling, not cutting. Same neighborhood, different family.
See a blade coming down. -cide names what it kills (suicide, pesticide); -cise/-cis names how it cuts (precise = cut to the exact edge, incise = cut in, excise = cut out). And to decide is to cut off every option but one.
Core Words Deep Dive
The few words from this family worth telling in full — one by one.
The teaching gem of this root. de- (off) + caedere (cut) literally means 'to cut off' — and what gets cut off are all the rival options. Imagine a branching set of paths; deciding is taking a blade to them and severing all but one. This is why decisive means clean and quick with the cut, and indecision is standing frozen with the knife still up. Most learners never connect decide to homicide, yet they share the same Latin blade.
prae- (in front) + cis (cut) = 'cut off at the front,' trimmed exactly to the edge with nothing hanging over. That image — a clean, deliberate cut leaving no excess — became the meaning 'exact, with no margin of error.' Compare concise, which is con- (thoroughly) + cis: cut all the way down to the essentials.
sui- (of oneself, from Latin sui) + cide (killing) = the killing of oneself. It is the clearest template for the whole -cide family: swap the victim at the front and you get homicide (a human), genocide (a people), patricide (one's father). The suffix -cide is constant; the prefix names who dies.
pest (a harmful creature) + -i- (connector) + cide (killer) = a substance that kills pests. This is the modern, industrial use of the root: chemists used -cide like a factory stamp to name killers of whole categories — herbicide kills plants, insecticide kills insects, fungicide kills fungi, bactericide kills bacteria. Here -cide means 'killer-of,' a thing rather than a deed.
in- (into) + cis (cut) + -ion (act) = the act or result of cutting into something, most often a surgeon's deliberate cut into skin. The same in- + cis gives incise (to cut into / engrave) and incisor (the front tooth that cuts food). Contrast excision: ex- (out) + cis = cutting something out and removing it.
Related Roots
cid (caedere) means cut/kill: decide, precise, homicide, pesticide. cad (cadere) means fall: accident, incident, coincidence, cadence. They look almost identical in spelling and both surface as -cid- in some words, but they are unrelated. Quick test: a blade is involved → cid; something drops or happens → cad.
Both relate to cutting, but sect (secare) is the everyday 'cut into parts' root — section, dissect, bisect, insect (an animal 'cut into' segments). cid/cis (caedere) carries the sharper edge of cutting off, cutting out, or striking dead: excise, incision, homicide. Dividing into pieces → sect; severing or killing → cid.
Associated Words · 44
bactericide
A substance that kills bacteria
chisel
A sharp-bladed tool for cutting stone, wood, or metal; to cut with such a tool
concise
Brief yet complete; expressing much in few words
concisely
Briefly and clearly, using few words
concision
Brevity and clarity of expression
decide
to make a choice or come to a conclusion
decided
Firm and resolute; clear and unmistakable
decidedly
Clearly and without doubt; in a resolute manner
decision
a choice made after thinking about options
decision-maker
A person who makes important decisions
decision-making
The process of choosing between options
decisive
Having a conclusive effect; able to make firm decisions quickly
decisively
In a firm and resolute manner
decisiveness
The quality of making decisions quickly and firmly
excide
To cut off or remove by cutting
excise
A domestic tax on goods; to impose such a tax or remove by cutting
excision
Surgical removal of tissue; deletion of text
excisional
Relating to or performed by surgical excision
fungicide
A substance used to kill or prevent the growth of fungi
genocidal
Relating to or constituting genocide
genocide
The deliberate mass destruction of an ethnic or national group
herbicide
A chemical used to kill unwanted plants
homicide
The killing of one person by another; a person who kills
imprecise
Not exact or accurate; vague
imprecisely
In an inexact or inaccurate manner
imprecision
Lack of exactness or accuracy
incise
To cut into a surface; to carve or engrave
incision
A cut made into something, especially a surgical cut
incisive
Intelligently analytical and forcefully direct in expression
incisor
A sharp front tooth used for cutting food
indecision
Inability to make a decision
indecisive
Unable to make firm decisions; not producing a clear result
indecisively
Without firmness or a clear outcome
indecisiveness
Tendency to be unable to make firm decisions
insecticide
A chemical substance used to kill insects
patricide
The murder of one's father; one who kills their father
pesticide
A chemical used to kill harmful insects or pests
precise
Exact and accurate in every detail; 精确的；准确的
precisely
In an exact and accurate manner; exactly right; 精确地；恰好
precision
The quality of being exact and accurate
scissors
A tool with two blades used for cutting
suicidal
Relating to or likely to commit suicide; extremely dangerous or self-destructive
suicide
The act of intentionally killing oneself; a person who has done so
undecided
Not yet settled or resolved; not having made up one's mind