ann

The root ann comes from Latin annus, meaning 'year.' For the Romans a year was the basic cycle of life — the time the earth took to come full circle — so annus became the building block for almost every word about things that repeat on a yearly rhythm.

Start with the plainest member:

- annual = happening once a year, or covering a year. An annual report sums up a whole year; an annual meeting comes round once each year.
- annually = the adverb: paid annually, meets annually.

From 'a year' it's a short step to 'a yearly payment':

- annuity = a fixed sum paid every year (often a pension). The word literally promises you something year after year.

And to 'a yearly record':

- annals = history written year by year. Ancient chroniclers logged events one year at a time, so the annals of history are the year-by-year books of the past.

Now the number prefixes multiply the years. Here the root usually shifts its spelling to -enn- inside a compound (because ann sits after another root and the vowel changes):

- bi- (two) + enn → biennial = every two years (or a plant that lives two years).
- cent (hundred) + enn → centennial = a hundredth anniversary.
- per- (through) + enn → perennial = lasting through all the years. A perennial plant survives year after year instead of dying each winter; a perennial problem is one that keeps coming back every year.

The thousand uses the longer form -enni-:

- mille (thousand) + enni → millennium = a span of a thousand years (plural millennia).

Finally, a less obvious one:

- super- (beyond) + annus → superannuated = beyond one's years, i.e. too old to keep working — retired, or by extension, outdated and obsolete.

So the family splits cleanly: bare ann/annu gives you year-words (annual, annuity, annals); the variant -enn- shows up wherever a number prefix stacks on top of 'year' (biennial, centennial, perennial, millennium). Spot -enn- and you've spotted annus in disguise.