Arctic ruminant (8)
I believe the answer is:
reindeer
'arctic ruminant' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for reindeer that I've seen before include "They pull Santa's sleigh" , "Arctic ruminant" , "'Dancer or Prancer, say (8)'" , "Red-nosed Rudolf is one" , "Rudolph, say" .)