No reduction in jam, accommodating a large yearning (9)
I believe the answer is:
nostalgic
'yearning' is the definition.
(thesaurus)
'no reduction in jam accommodating a large' is the wordplay.
'reduction in' means to remove the last letter (the number of letters in the word is reduced).
'jam' becomes 'stick' (jam can mean to get stuck).
'accommodating' indicates putting letters inside.
'large' becomes 'lg' (abbreviation).
'stick' with its last letter taken off is 'stic'.
'a'+'lg'='alg'
'stic' enclosing 'alg' is 'stalgic'.
'no'+'stalgic'='NOSTALGIC'
(Other definitions for nostalgic that I've seen before include "Fondly remembering the past" , "down Memory Lane" , "Yearning for the past" , "longing for home" , "Sentimental about the past" .)