WordNet sense 1 (something that bulges out or is protuberant or projects from its surroundings):

bulge, bump, excrescence, extrusion, jut, prominence, protrusion, protuberance, gibbosity, gibbousness

WordNet sense 2 (arch one's back):

hunch, hunch forward, hunch over

WordNet sense 3 (have sexual intercourse with):

bang, bed, jazz, know, love, screw, bonk, make out, be intimate, do it, get laid, have sex, make love, roll in the hay, sleep with, eff, get it on, have a go at it, have intercourse, have it away, have it off, lie with