Not at the start of the year for me. I just confirmed my Office 365 is up to date (in fact, it did install the latest update when I checked). Right-click/Menu key -> Synonyms still works to show a list as does SHft+F7 to bring up the full list.
Can anyone clarify who this affects?
Oh, and I do now get a hovering Copilot icon in Word's margin when I do that (never seen that before). So it does appear that the Theasurus remains even after getting Copilot.
I think
@D0nH0ward must be right and it's not the Thesaurus that's going away, but just SmartLookup. Losing Thesaurus would be bad, but losing SmartLookup doesn't bother me. I never found its lookup features particularly usable. Faster to use Thesaurus or just look the word up in a standalone dictionary (and better definitions).
I would like it if Word added a full offline dictionary with instant definition lookup that I could access with a keypress (OFFLINE), but I don't think it's ever had that.