Ultimately from Arabic حَنَك (ḥanak, “jaw”), in some dialects via Northern Kurdish henek (“joke”). The sense development is ‘jaw, chin’ → ‘gab, chitchat, chinwag’ → ‘joke’. For such a development compare Turkish çene (“chin; talkativeness”) and Central Kurdish گاڵتە و گەپ (gallte û gep, “gossip; chitchat, fun conversation”, literally “joke and cheek”).