New in terrain, having time (6)
I believe the answer is:
winter
'time' is the definition.
(time of year)
'new in terrain having' is the wordplay.
'having' says the answer is hidden in the clue.
'WINTER' is hidden in the letters of 'new in terrain'.
(Other definitions for winter that I've seen before include "Cold season" , "period of freeze?" , "Cold period" , "'Now is the . . . . . . of our discontent' (Richard III)" , "Time for mittens and scarves?" .)