Protuberate comes from Late Latin protuberatus, past participle of protuberare ('to swell out'), from Latin pro- ('forth') + tuber ('lump, swelling'). The historical chain includes Latin protuberare and Latin tuber. The quoted older senses, "to swell out", "forth", and "lump, swelling", supply the semantic anchors for protuberate. The formation is best read as compound, participial, and borrowed: the word protuberate carries its older form-history into a compact English lexical shape. In present English it is used as a verb, "to bulge out or project beyond a surface". English derivatives include protuberation; related English forms include protuberance, protuberant, and tuber. The result is a verb whose etymology preserves both the older form and the later English specialization.