sebaceous secretion, 1819, from Latin, from Greek smegma "a detergent, soap, unguent," from smekhein "to wipe off, wipe clean, cleanse," from PIE root *sme- "to smear" (cognates: Czech smetana "cream," and see smear, v.). So called from resemblance; a medical coinage, the word seems not to have been used in its literal Greek sense in English before this. Related: Smegmatic.