Stop mostly domesticated chicken (6)
I believe the answer is:
bantam
'chicken' is the definition.
(bantam is a kind of chicken)
'stop mostly domesticated' is the wordplay.
'stop' becomes 'ban' (I've seen this in other clues).
'mostly' means to remove the last letter (most but not all of the word).
'domesticated' becomes 'tame' (similar in meaning).
'tame' with its last letter removed is 'tam'.
'ban'+'tam'='BANTAM'
(Other definitions for bantam that I've seen before include "Nab mat (anag)" , "Diminutive breed of hen" , "Little clucker" , "Aggressive person" , "Half of 1D [GAME OR BIRD]" .)