Finish after only half the distance and stretch out (7)
I believe the answer is:
distend
'stretch out' is the definition.
(I've seen this in another clue)
'finish after only half the distance' is the wordplay.
'finish' becomes 'end' (synonyms).
'after' says to put letters next to each other.
'only half' suggests halving the letters.
'distance' halved is 'dist'.
'end' after 'dist' is 'DISTEND'.
'and' acts as a link.
(Other definitions for distend that I've seen before include "Make you bulge" , "Expand, inflate" , "Bloat" , "Swell with internal pressure" , "balloon" .)