Gossip is good when appropriate (6)
I believe the answer is:
gasbag
'gossip' is the definition.
(I've seen this before)
'good when appropriate' is the wordplay.
'good' becomes 'g' (abbreviation).
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'appropriate' becomes 'bag' (I've seen this in other clues).
'g'+'as'+'bag'='GASBAG'
'is' acts as a link.
(Other definitions for gasbag that I've seen before include "One who talks too much, or a balloon" , "One talks incessantly about trivial things" , "One talks at length on boring topics" , "One who natters a lot" , "I can't shut up" .)