Yawns, concealing origin of rotting fruit (6)
I believe the answer is:
grapes
'fruit' is the definition.
(I've seen this before)
'yawns concealing origin of rotting' is the wordplay.
'yawns' becomes 'gapes' ('gape' can be a synonym of 'yawn').
'concealing' means one lot of letters goes inside another.
'origin of' suggests taking the first letters.
The first letter of 'rotting' is 'r'.
'gapes' enclosing 'r' is 'GRAPES'.
(Other definitions for grapes that I've seen before include "See 10 Across" , "They grow on vines" , "Source of wine" , "Fruit for wine" , "'Green, black or purple clusters (6)'" .)