Embarrassment of companion ends with a smile (7)
I believe the answer is:
chagrin
'embarrassment' is the definition.
(chagrin is a kind of embarrassment)
'companion ends with a smile' is the wordplay.
'companion' becomes 'ch' (I've seen this in other clues).
'ends' says to put letters next to each other.
'with' is a charade indicator (letters next to each other).
'smile' becomes 'grin' (grinning is a kind of smiling).
'ch'+'a'+'grin'='CHAGRIN'
'of' acts as a link.
(Other definitions for chagrin that I've seen before include "Arching with annoyed disappointment" , "Strong feeling of embarrassment" , "Shame at one's failure" , "Annoy" , "Frustration at having failed" .)