eg sole four-letter word, in itself, is harmless (4)
I believe the answer is:
fish
'eg sole' is the definition.
(I know that sole is a type of food fish)
'four-letter word in itself is harmless' is the wordplay.
'four-letter word in' indicates the answer is hidden within the clue.
'FISH' is hidden in the letters of 'itself is harmless'.
(Other definitions for fish that I've seen before include "- - and chips" , "Aquatic animal" , "counter in various games" , "Trawler's catch" , "Aquatic creature; rail-joining plate" .)