In time a Greek may be thin (6)
I believe the answer is:
meagre
'be thin' is the definition.
(thesaurus)
'in time a greek' is the wordplay.
'in' indicates a hidden word.
'MEAGRE' can be found hidden inside 'time a greek'.
'may' is the link.
(Other definitions for meagre that I've seen before include "weak" , "Insufficient; scanty" , "Insubstantial" , "Miserable" , "lacking in strength" .)