Somewhat critical, i.e., nitpicky visitor (5)
I believe the answer is:
alien
'visitor' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'somewhat critical i e nitpicky' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'ALIEN' is hidden in the letters of 'critical i e nitpicky'.
Can you help me to learn more?
(Other definitions for alien that I've seen before include "Clanger?" , "exciting film based in space" , "Foreign; extraterrestrial" , "Outlandish" , "Foreign - film directed by Ridley Scott" .)