Underlines rhymes with:
enterline's, esterline's, airline's, airlines, airlines', baselines, bloodlines, caroline's, coastlines, dateline's, datelines, deadlines, enterline's, esterline's, felines, frontline's, guidelines, headlines, hemlines, hotlines, lifelines, moneyline's, nightline's, nightlines, online's, outlines, pipeline's, pipelines, pipelines', sidelines, skylines, smithkline's, storylines, strandlines, villines
Underlines sounds like:
underling, underlings, underlining, underlying