Greek airline no longer stores A to Z in this (7)
I believe the answer is:
pangram
'a to z in this' is the definition.
'greek airline no longer stores' is the wordplay.
'greek' becomes 'gr'.
'airline no longer' becomes 'panam' (Pan Am).
'stores' indicates putting letters inside.
'gr' put within 'panam' is 'PANGRAM'.
(Other definitions for pangram that I've seen before include ""The quick brown fox ..." for example" , "Text using whole alphabet" , "special literary construction" , "Sentence containing all twenty-six letters" .)