Small step in the final frontier (5)
I believe the answer is:
space
'the final frontier' is the definition.
The definition and answer can be both shapes as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'small step' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'step' becomes 'pace' (synonyms).
's'+'pace'='SPACE'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for space that I've seen before include "Room for capes" , "Expanse" , "Interstellar vacuum" , "A particular area for paces" , "sci-fi theme" .)