simplex (adj.)

"characterized by a single part," 1590s, from Latin simplex "single, simple, plain, unmixed, uncompounded," literally "onefold," from PIE compound of root *sem- (1) "one; as one, together with" + *plac- "-fold," from PIE root *plek- "to plait." The noun is attested from 1892, "simple uncompounded word."