Prohibit mostly domesticated chicken (6)
I believe the answer is:
bantam
'chicken' is the definition.
(bantam is a kind of chicken)
'prohibit mostly domesticated' is the wordplay.
'prohibit' becomes 'ban' (banning is a kind of prohibiting).
'mostly' means to remove the last letter (most but not all of the word).
'domesticated' becomes 'tame' (similar in meaning).
'tame' with its final letter taken away is 'tam'.
'ban'+'tam'='BANTAM'
(Other definitions for bantam that I've seen before include "Diminutive breed of hen" , "Nab mat (anag)" , "Small chicken - small soldier" , "Dwarf variety of domestic fowl" , "Supplier of eggs" .)