Prohibit domesticated, tailless fowl (6)
I believe the answer is:
bantam
'fowl' is the definition.
(bantam is a kind of fowl)
'prohibit domesticated tailless' is the wordplay.
'prohibit' becomes 'ban' (banning is a kind of prohibiting).
'domesticated' becomes 'tame' (similar in meaning).
'tailless' means to remove the last letter (the tail of the word is removed).
'tame' with its final letter taken off is 'tam'.
'ban'+'tam'='BANTAM'
(Other definitions for bantam that I've seen before include "Supplier of eggs" , "Aggressive person" , "Small chicken - small soldier" , "aggressive little sort" , "Small breed of chicken" .)