Mainlines are the primary routes or lines of communication, transportation or supply. The antonyms for the term mainlines imply either secondary or minor routes or no route at all. Some possible antonyms for mainlines include back roads, side roads, minor railways, branch lines. Offshoots, tributaries, feeders, lesser arteries, and auxiliary routes. These words all signify a lesser degree of importance as compared to Mainlines. Besides, antonyms for mainlines might also include terminus, stranded, stuck, or discontinued, indicating a lack of continuation or ending. In all, antonyms for mainlines denote secondary, minor or non-functional routes or destinations.