Smile awkwardly, maybe losing heart (4)
I believe the answer is:
beam
'smile' is the definition.
(to beam is to smile)
'awkwardly maybe losing heart' is the wordplay.
'awkwardly' is an anagram indicator.
'losing heart' says to hollow out the word (remove centre letters).
'maybe' with its centre removed is 'mabe'.
'mabe' with letters rearranged gives 'BEAM'.
(Other definitions for beam that I've seen before include "Smile broadly or radiate" , "Light - heavy timber - wide smile" , "Column of light" , "Gymnast's bar; broad smile" , "Apparatus used by women gymnasts" .)