undersurface

the side or part facing downward from something <painted the undersurface of the plane blue> Synonyms underbelly, underbody, underpart, underside, bottomRelated Words belly, sole, toe; base, floor, foot, ground, seat, underpinning; undercarriageNear Antonyms acme, apex, climax, crest, crown, culmination, height, high-water mark, meridian, peak, pinnacle, roof, summit; cusp, head, point, tip, tip-top, zenithAntonyms face, top