Feeble person (4)
I believe the answer is:
wimp
'feeble person' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for wimp that I've seen before include "Informally, an ineffectual man" , "Unassertive person" , "Feeble or ineffectual person" , "Informally, an ineffective man" , "Weak individual" .)