Second time in straw is fast (5)
I believe the answer is:
hasty
'is fast' is the definition.
(thesaurus)
'second time in straw' is the wordplay.
'second' becomes 's' (common abbreviation).
'time' becomes 't' (abbreviation).
'in' indicates putting letters inside.
'straw' becomes 'hay' (I've seen this before).
's'+'t'='st'
'st' put inside 'hay' is 'HASTY'.
(Other definitions for hasty that I've seen before include "Rash; hurried" , "Hurried; without thinking" , "Speedy" , "Reckless; hurried" , "Rashly quick" .)