Quick, a stay (5)
I believe the answer is:
alive
'quick' is the definition.
(thesaurus)
'a stay' is the wordplay.
'stay' becomes 'live' (**).
'a'+'live'='ALIVE'
(Other definitions for alive that I've seen before include "Spirited" , "Still with us" , "Extant" , "full of vitality" , "Breathing, existing" .)