Manly coat how short? (5)
I believe the answer is:
macho
'manly' is the definition.
(I've seen this before)
'coat how short?' is the wordplay.
'coat' becomes 'mac' (mac is a kind of coat).
'short?' means to remove the last letter (I've seen 'shorter' mean this).
'how' with its final letter removed is 'ho'.
'mac'+'ho'='MACHO'
(Other definitions for macho that I've seen before include "Butch" , "Ramboesque" , "Like aggressive male" , "Ostentatiously virile" , "Spiny lobster" .)