A year ending in December is what you'd expect (3)
I believe the answer is:
par
'what you'd expect' is the definition.
(par for the course)
'a year ending in december' is the wordplay.
'a year' becomes 'pa' (per annum).
'ending in' suggests the final letters.
The final letter of 'december' is 'r'.
'pa'+'r'='PAR'
'is' acts as a link.
(Other definitions for par that I've seen before include "Norm" , "Rating of strokes required for hole (golf)" , "Usual or expected level" , "standard for a pro" , "Accepted standard" .)