BOUT ENDERS is a term used in boxing to refer to the last round of a match. The crossword solutions KAYOS (5 letters), KOS (3 letters) and TKOS (4 letters) are all related to this term. KAYOS is an alternate spelling of the word 'KAYO', which is a slang term for a KNOCKOUT punch. KOS is an abbreviation for 'KNOCKOUT', while TKOS stands for 'technical KNOCKOUT'. All three terms refer to a boxer being knocked out by their opponent, thus ending the bout.