Time mare becomes less wild (5)
I believe the answer is:
tamer
'less wild' is the definition.
('tame' can be the opposite of 'wild' so perhaps 'tamer' is reasonable for 'less wild')
'time mare becomes' is the wordplay.
'time' becomes 't' (abbreviation).
'becomes' indicates an anagram.
'mare' anagrammed gives 'amer'.
't'+'amer'='TAMER'
(Other definitions for tamer that I've seen before include "Less arousing, exciting" , "Less wild" , "Animal trainer" , "less offensive?" .)