the word 'trotline' is an american english compound, first attested in the early 19th century. its first element, 'trot', presents an etymological puzzle; it is not directly from the verb meaning 'to move at a pace between a walk and a run'. one plausible theory suggests it may derive from a regional or dialectal use of 'trot' meaning a route or a beat, akin to a patrol, reflecting the action of moving along the line to tend it. the second element, 'line', has a clear lineage from old english, ultimately from the latin 'līnea', originally a thread made from flax. the compound thus logically names a fishing apparatus consisting of a main line, which one might periodically 'trot' along to check, set with multiple baited hooks.

this is a compound noun formed from two english words, but its specific formation is considered a single lexical unit in modern usage. the first element is 'trot', a term of uncertain origin in this context, possibly related to a trot or a steady pace, referring to the method of checking the line. the second element is 'line', from old english 'līne' (rope, series), from latin 'līnea' (linen thread, string).