Origin and history of translucent

"presenting no obstacle to the passage of light, so that what is behind can be distinctly seen," early 15c., transparente, from Medieval Latin transparentem (nominative transparens), present participle of transparere "show light through," from Latin trans "across, beyond; through" (see trans-) + parere "come in sight, appear; submit, obey" (see appear).

The figurative pejorative sense of "easily seen through, manifest, obvious" is attested by 1590s; the more positive sense of "frank, open, candid" is by 1580s. The attempt to back-form a verb transpare "appear through something else" (c. 1600) is in Blount but died with the 17c. Related: Transparently.

     That is diaphanous which does not preclude sight of what is behind it ; garments, vapour, membrane ; opp. shrouding.

     That is transparent which does not even obscure sight of what is behind it ; glass, candour, pretence ; opp. obscuring.

     That is pellucid which does not distort images seen through it ; water, literary style ; opp. turbid.

     That is translucent which does not bar the passage of light ; alabaster, tortoise-shell ; opp. opaque.

[Fowler, "Modern English Usage," 1926]

early 15c., "faint or indistinct light," a sense now obsolete, from Medieval Latin translucentia, from Latin translucentem (see translucent). By 1755 as "partial transparency to light" (earlier in this sense translucency, 1620s). By 1826 as "act or fact of shining through."