Clue: Chestnut, one in traditional hunt (5)
Answer: CHACE
Explanation: Definition: traditional hunt
CH + ACE – variant of "chase". ~~CH = chestnut must be the abbreviation that Chanbers dosn't give, as mentioned in the rubric; I couldn't find any justification of it online, and I don't know if it's used in the context of trees, horses, or something else~~ *Ignore this – I looked again in Chambers and there it was. See 6d for the actual missing abbreviation.