transparent (adj.)

late 13c., "come into view," from stem of Old French aparoir, aperer "appear, come to light, come forth" (12c., Modern French apparoir), from Latin apparere "to appear, come in sight, make an appearance," from ad "to" (see ad-) + parere "to come forth, be visible; submit, obey," which is of uncertain origin; de Vaan says from a PIE *prh-o- "providing."

Of persons, "present oneself," late 14c. The meaning "seem, have a certain appearance" is late 14c. Related: Appeared; appearing.

1610s, "condition of being transparent, perviousness to light," from Medieval Latin transparentia, from transparentem (see transparent). The meaning "that which is transparent" is from 1590s. In reference to pictures, prints, etc., intended to be seen by means of transmitted light, from 1785; in photography, of a positive picture on glass intended to be viewed by transmitted light, from 1866. Related: Transparence (1590s).

word-forming element meaning "across, beyond, through, on the other side of; go beyond," from Latin trans (prep.) "across, over, beyond," perhaps originally present participle of a verb *trare-, meaning "to cross," from PIE *tra-, variant of root *tere- (2) "cross over, pass through, overcome" [Watkins].

Besides its use in numerous English words taken from Latin words with this prefix, it is used to some extent as an English formative .... It is commonly used in its literal sense, but also as implying complete change, as in transfigure, transform, etc. [Century Dictionary]

In chemical use indicating "a compound in which two characteristic groups are situated on opposite sides of an axis of a molecule" [Flood].

Many trans- words in Middle English via Old French arrived originally as tres-, due to sound changes in French, but most English spellings were restored later; trespass and trestle being exceptions.