Answer in half minute: pipe (4)
I believe the answer is:
main
'pipe' is the definition.
(main is a kind of pipe)
'answer in half minute' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'in' is an insertion indicator.
'half' suggests halving the letters.
'minute' cut in half is 'min'.
'a' placed within 'min' is 'MAIN'.
(Other definitions for main that I've seen before include "(The mighty) sea" , "Chief - principal electricity cable" , "Source of water" , "Cardinal" , "Dominant" .)