Small step into opening (5)
I believe the answer is:
space
'opening' is the definition.
(I've seen this in another clue)
'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 "Emptiness" , "Gap between words" , "sci-fi theme" , "A particular area for paces" , "Cosmos" .)