WordNet sense 1 (the second half of an inning; while the home team is at bat):

bottom of the inning

WordNet sense 2 (low-lying alluvial land near a river):

bottomland

WordNet sense 3 (a depression forming the ground under a body of water):

bed

WordNet sense 4 (the lower side of anything):

underside, undersurface

WordNet sense 5 (the fleshy part of the human body that you sit on):

backside, behind, bum, buns, buttocks, can, derriere, fanny, hindquarters, posterior, rear, rump, seat, stern, tail, tush, arse, fundament, keister, nates, prat, tooshie, tush, tail end, hind end

WordNet sense 6 (a cargo ship):

freighter, merchantman, merchant ship

WordNet sense 7 (come to understand):

fathom, penetrate

WordNet sense 8 ((superlative of `bad') most wanting in quality or value or condition):

worst