interval n.

word-forming element used freely in English, "between, among, during," from Latin inter (prep., adv.) "among, between, betwixt, in the midst of" (also used extensively as a prefix), from PIE *enter "between, among" (source also of Sanskrit antar, Old Persian antar "among, between," Greek entera (plural) "intestines," Old Irish eter, Old Welsh ithr "among, between," Gothic undar, Old English under "under"), a comparative of root *en "in."

A living prefix in English from 15c. and used with Germanic as well as Latinate words. Spelled entre- in French; most words borrowed into English in that form were re-spelled 16c. to conform with Latin except entertain, enterprise. In Latin, spelling shifted to intel- before -l-, hence intelligence, etc.

Old English weall, Anglian wall "rampart, dike, earthwork" (natural as well as man-made), "dam, cliff, rocky shore," also "defensive fortification around a city, side of a building," an Anglo-Frisian and Saxon borrowing (Old Saxon, Old Frisian, Middle Low German, Middle Dutch wal) from Latin vallum "wall, rampart, row or line of stakes," apparently a collective form of vallus "stake," from PIE *walso- "a post." Swedish vall, Danish val are from Low German.

Meaning "interior partition of a structure" is mid-13c. In this case, English uses one word where many languages have two, such as German Mauer "outer wall of a town, fortress, etc.," used also in reference to the former Berlin Wall, and wand "partition wall within a building" (compare the distinction, not always rigorously kept, in Italian muro/parete, Irish mur/fraig, Lithuanian mūras/siena, etc.). The Latin word for "defensive wall" was murus (see mural).

Anatomical use from late 14c. To give (someone) the wall "allow him or her to walk on the (cleaner) wall side of the pavement" is from 1530s. To turn (one's) face to the wall "prepare to die" is from 1570s. Phrase up the wall "angry, crazy" is from 1951; off the wall "unorthodox, unconventional" is recorded from 1966, American English student slang. To go over the wall "escape" (originally from prison) is from 1933. Wall-to-wall (adj.) recorded 1939, of shelving, etc.; metaphoric use (usually disparaging) is from 1967.