Yup, exact same thing - annulus being the Latin diminutive

Similar process with "homunculus" (little man) and "calculus" (little rock) and "nucleus" (little nut).

Huh. "Nucleus" is a form that looks like an adjective to me; I'd expect "nucula" for the diminutive of "nux".

And indeed I see this on etymonline:

> from Latin nucleus "kernel," from nucula "little nut," diminutive of nux (genitive nucis) "nut,"

So for whatever reason a new word was called for, and our nucleus comes from that, not from the diminutive form of "nut".

And events that take place yearly are called annual. Not to mention abbreviations like AD for "anno domini," the year of the lord.