longline Syllabification: (long·line)Pronunciation: /ˈlôNGˌlīn, ˈläNG-/Definition of longline noun a type of deep-sea fishing gear consisting of a long main line anchored to the bottom to which shorter lines with baited hooks are fastened at intervals: [as modifier]:a longline fishing boatlongline in other Oxford dictionaries Definition of longline in the British & World English dictionary