A step made quickly (5)
I believe the answer is:
apace
'quickly' is the definition.
(I know that quickly can be written as apace)
'a step' is the wordplay.
'step' becomes 'pace' (pace is a kind of step).
'a'+'pace'='APACE'
'made' acts as a link.
(Other definitions for apace that I've seen before include "at high speed" , "What's quickly" , "Quick" , "(Move on) swiftly" , "flat out" .)