Desire a new T-shirt (6)
I believe the answer is:
thirst
'desire' is the definition.
(I know that thirst is a type of desire)
'a new t-shirt' is the wordplay.
'a new' indicates anagramming the letters.
't'+'shirt'='tshirt'
'tshirt' anagrammed gives 'THIRST'.
(Other definitions for thirst that I've seen before include "Hunger" , "Need for liquids" , "Want of drink" , "Quaff to slake it" , "Long" .)