Tattoo

tattoo \ta-ˈtü\ noun: 1. a rapid rhythmic rapping,
2. a call sounded shortly before taps as notice to go to quarters, 3. outdoor military exercise given by troops as evening entertainment
transitive verb: to beat or rap rhythmically on; drum on
intransitive verb: to give a series of rhythmic taps

Etymology: alteration of earlier taptoo, from Dutch taptoe, from the phrase tap toe! taps shut!

tattoo \ta-ˈtü\ noun: 1. an indelible mark or figure fixed upon the body by insertion of pigment under the skin, 2. the act of marking thusly or the fact of being thusly marked
transitive verb: to mark or color the skin with a tattoo

Etymology: Tahitian tatau tattoo (noun)

Homonyms are two or more words that are spelled and pronounced alike but that differ in meaning. Tattoo in its wildy divergent meanings and etymologies is a striking example of a homonym.