I have it on reasonably good authority (though a long ago one) that voluptuous and volunteer have their origins in the same word. I can’t remember what that word is, but I always thought this information was amusing. I’m sharing this tidbit after forty years.
c.1374, “of desires or appetites,” from O.Fr. voluptueux, from L. voluptuosus “full of pleasure, delightful,” from voluptas “pleasure, delight,” from volup “pleasurably,” perhaps ultimately related to velle “to wish,” from PIE *wol-/*wel- “be pleasing” (see will (v.)). Meaning “addicted to sensual pleasure” is recorded from c.1440. Sense of “suggestive of sensual pleasure” is attested from 1816 (Byron); especially in ref. to feminine beauty from 1839. Voluptuary “one addicted to sensuous pleasures” is attested from 1610.