Web story not revealing a nark (6)
I believe the answer is:
nettle
'nark' is the definition.
(I know that nark can be written as nettle)
'web story not revealing a' is the wordplay.
'web' becomes 'net' (synonyms).
'story' becomes 'tale' (synonyms).
'not revealing' is a deletion indicator.
'tale' with 'a' taken out is 'tle'.
'net'+'tle'='NETTLE'
(Other definitions for nettle that I've seen before include "Common stinging plant" , "Plant to irritate" , "Annoy - stinger" , "Plant with stinging hairs" , "To be annoying" .)