Ascend is Latin ascendere, "to climb up," built from ad, "to," plus scandere, "to climb." Here the prefix did not double the following consonant, because sc- resisted it, so the word keeps a visible ad- worn down to a-. It belongs to a tidy set English borrowed whole: ascend, descend, transcend and condescend all carry the same scandere, and none of them mean anything like "climb" in ordinary use any more.
English took it in the late 1300s, already meaning "move upward," and the astronomical sense — of planets and constellations coming over the horizon — came with it from Latin. The gentler modern sense of a road or slope rising is surprisingly late, only 1832. Old English had its own perfectly good word for the action, stigan, which survives in disguise in stile and in the sty you can get in your eye; it lost out to the borrowed one, which is the usual story.
ascend (v.) late 14c., ascenden , "move upward," from Latin ascendere "climb up, mount," of planets, constellations, "come over the horizon," figuratively "to rise, reach;" from ad "to" (see ad- ) + scandere "to climb" (see scale (v.1)). The meaning "slope upward" is from 1832. Related: Ascended ; ascending . An Old English word for it was stigan (see sty (v.)). also from late 14c.
ascend came in through Latin, and its spelling follows that family's conventions.
On the register ladder
English kept all three words for this idea, one from each layer, and the rung is itself the cue: the native word is blunt and concrete, the French one polite, the Latin one formal or technical.
| Old English | French | Latin |
|---|---|---|
| rise | mount | ascend |