Small head in flood (5)
I believe the answer is:
spate
'flood' is the definition.
(synonyms)
'small head' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'head' becomes 'pate' (humorous term for the head).
's'+'pate'='SPATE'
'in' acts as a link.
(Other definitions for spate that I've seen before include "Sudden forceful flow" , "A torrent of tapes" , "Sudden river flood" , "Sudden increased quantity" , "Tapes found in sudden flood" .)