Burn small spike (4)
I believe the answer is:
sear
'burn' is the definition.
(thesaurus)
'small spike' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'spike' becomes 'ear' ('ear' can be a synonym of 'spike'**).
's'+'ear'='SEAR'
(Other definitions for sear that I've seen before include "Burn briefly" , "Burn, scorch intensely" , "Cauterise" , "Scorch, brand" , "Cauterize" .)