Inflate article during ascent (5)
I believe the answer is:
raise
'inflate' is the definition.
(I've seen this in another clue)
'article during ascent' is the wordplay.
'article' becomes 'a' (English indefinite article).
'during' means one lot of letters goes inside another.
'ascent' becomes 'rise' (synonyms).
'a' put within 'rise' is 'RAISE'.
(Other definitions for raise that I've seen before include "Advance" , "Gather" , "Produce" , "Erect; grow" , "Hoist" .)