MAKING DO

In Latin, the fourth principal part of the verb agere, meaning "to do", was actus, which could best be translated as "having been done". Actus has had an outsized influence on the English language, making up a lot of words starting with act-:

• Through the twelfth century Old French word actif, it gave us the word active, since being active is doing something
• Through the thirteenth century Old French word actuel, meaning "up to date", it gave us actual, since something that is done is up to date and something that is up to date is actual or existing.
• Act and actor both came directly from Latin between the late 1300s and mid 1400s, because an act was something that was done and an actor was a person who did something

And, of course, many of these words have their own derivatives. It's crazy to think how one conjugation of an old verb could have such an impact on how we speak today.