Twelve months (4)
'twelve months' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for year that I've seen before include "Complete cycle of seasons" , "One tenth of a decade" , "eg 2004" , "See 33 Across" , "Orbital period" .)
'twelve months' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for calendar year that I've seen before include "period of months?" , "January 1 to December 31 inclusive" , "Twelve months" .)