Small step into void (5)
I believe the answer is:
space
'void' is the definition.
(thesaurus)
'small step' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'step' becomes 'pace' (synonyms).
's'+'pace'='SPACE'
'into' is the link.
(Other definitions for space that I've seen before include "Cosmos" , "Interstellar region" , "Emptiness" , "Expanse" , "Unfilled region" .)