The term 'lock horns' is an idiom that means to ARGUE or fight. The crossword solutions for this term include 'ARGUE' (5 letters), 'TANGLE' (6 letters), 'SCRAP' (5 letters), 'VIE' (3 letters), 'SPAR' (4 letters), 'CLASH' (5 letters), 'ENGAGE' (6 letters), 'COMPETE' (7 letters), 'DISPUTE' (7 letters), and 'STRUGGLE' (8 letters). All of these words are related to the idea of conflict, and the last solution, 'bumphheads' (9 letters), is a slang term for two people who are arguing.