Pair in sunlit wood (3)
I believe the answer is:
two
'pair' is the definition.
(a pair means two of something)
'in sunlit wood' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TWO' can be found hidden inside 'sunlit wood'.
(Other definitions for two that I've seen before include "Fifth root of thirty-two" , "Old song 'Tea for . . .'" , "Number in pair" , "A pair (3)" , "Number of faces of the god Janus" .)