gress

The root gress comes from one of the most physical ideas in Latin: putting one foot in front of the other. The verb gradi meant "to step, to walk," and its noun gradus meant "a step" — both the footstep you take and the step of a staircase. From a single image of walking, Latin built a whole map of movement, and the prefix always tells you which way the feet are pointing.

Go forward and you make pro-gress (pro- 'forward' + gress). Turn around and walk back and you re-gress (re- 'back'). Walk back even further, the old-fashioned way, and you retro-grade (retro- 'backward'). When people walk toward one place and gather, that is con-gress (con- 'together') — literally a "walking-together," which is exactly what a Congress of representatives is. Step across a boundary you shouldn't cross and you trans-gress (trans- 'across') — to sin, to break a rule. Wander off the straight path of your topic and you di-gress (dis- 'aside'). And when you walk in or out of a place, you have in-gress (entry) and e-gress (exit).

One member surprises people: aggressive. It is ad- 'toward' + gradi 'to step.' To be aggressive is to step toward someone — and stepping toward a person, in the old military sense, meant advancing on them, attacking. The hostility is baked into the direction of the walk.

The other half of the family uses the variant grad-/gred- and leans on gradus as "a step" in the sense of a rung or level. A grade is a level. To do something gradual is to move one small step at a time. A degree (de- 'down' + gradus) was originally a single step down a series — which is why we still measure temperature, angles, and academic rank in "degrees." To graduate is to step up through the ranks of a school. And the surprise member here is ingredient: in- 'into' + gradi 'to walk' — an ingredient is literally something that "walks into" the mixing bowl. The grad- branch even reaches a kitchen.

So the whole family is one verb of walking, bent in every direction by its prefix: forward, back, across, together, in, out, up the rungs.