bosom (n.) Look up bosom at Dictionary.com
Old English bosm "breast; womb; surface; ship's hold," from West Germanic *bosm- (source also of Old Frisian bosm, Old Saxon bosom, Middle Dutch boesem, Dutch boezem, Old High German buosam, German Busen "bosom, breast"), perhaps from PIE root *bhou- "to grow, swell," or *bhaghus "arm" (in which case the primary notion would be "enclosure formed by the breast and the arms").

Bosoms in the narrowed or euphemistic meaning "a woman's breasts" is from 1959; bosomy "big-breasted" is from 1928. Bosom-friend is attested 1580s; bosom buddy from 1920s. Abraham's bosom "the abode of the blessed" is from Luke xvi.19-31.