Quickly take a step (5)
I believe the answer is:
apace
'quickly' is the definition.
(synonyms)
'a step' is the wordplay.
'step' becomes 'pace' (pace is a kind of step).
'a'+'pace'='APACE'
'take' acts as a link.
(Other definitions for apace that I've seen before include "flat out" , "(Move on) swiftly" , "At a rapid rate" , "at high speed" , "What's quickly" .)