I encountered this word just now in the book I am reading. Shanks (of revered memory)
used it a couple times in distant pass. I think it a useful word in that it has a shade of
meaning for which I cannot at the moment think of a good alternative. It means to notice,
but usually with an unfavorable eaction. I hope it will not become obsolete.

Here's the MW synonym entry for animadversion:

Entry Word: animadversion
Function: noun
Text: a remark or statement that constitutes an adverse and usually uncharitable criticism <her spiteful animadversions on her neighbors' children>
Synonyms aspersion, obloquy, reflection, slam, slur, stricture
Related Word censure, criticism, reprehension; accusation, imputation, insinuation; captiousness, carping, caviling, faultfinding
Contrasted Words acclaim, extolling, laudation, praise; approbation, approval
Antonyms commendation