Bosom comes from Old English bōsm ('bosom, breast, lap'), from Proto-Germanic *bōsmaz, of uncertain further origin, perhaps from Proto-Indo-European *bʰō- ('to grow, swell'). The historical trail runs through bōsm in Old English and *bōsmaz in Proto-Germanic. The history must be left partly open, preserving the uncertainty rather than forcing a single unsupported ancestry. Used as a noun and adjective, bosom now means "the chest or breast, especially as the seat of emotion; close and intimate", so the present definition can be read against the older forms and meanings. The same lexical family is also visible in derived forms such as bosomy. That uncertainty is part of the entry: the safest account is the attested form and the limited comparisons preserved with it.