scrimshaw n.

"shell or piece of ivory fancifully carved," a sailor's word, by 1864 in that spelling, also scrimshon, etc., "A nautical word of unstable orthography" [Century Dictionary]; a back-formation from American English scrimshander ("Moby Dick," 1851), scrimshonting (1825), which is of obscure origin. Scrimshaw is an English surname, attested from mid-12c., from Old French escremisseor "fencing-master." As a verb, by 1883.