1412 (implied in penetrable), from L. penetratus, pp. of penetrare "to put or get into, enter into," related to penitus "within, inmost," penus "innermost part of a temple, store of food," penates "household gods." Penetration is first attested 1605, from L. penetrationem (nom. penetratio) "a penetrating or piercing," from penetrare. The sexual sense is attested from 1613. Penetrating in the fig. sense of "touching the feelings intensely" is attested from 1632.