lean-to (n.)

c. 1200, from Old English hlinian "to recline, lie down, rest; bend or incline" (Mercian hleonian, Northumbrian hlionian), from Proto-Germanic *hlinen (source also of Old Saxon hlinon, Old Frisian lena, Middle Dutch lenen, Dutch leunen, Old High German hlinen, German lehnen "to lean"), from PIE root *klei- "to lean."

Transitive sense "cause to lean or rest" is from 14c. Meaning "to incline the body against something for support" is mid-13c. Figurative sense of "to trust for support" is from early 13c. Sense of "to lean toward mentally, to favor" is from late 14c. Related: Leaned; leaning. Colloquial lean on "put pressure on" (someone) is first recorded 1960.

c. 1300, pentis, pendize, "a shed or sloping roof projecting from a main wall or the side or end of a building," from Anglo-French pentiz, a shortening of Old French apentis "attached building, appendage," from Medieval Latin appendicium, from Latin appendere "to hang" (see append).

The modern spelling is from c. 1530 by folk etymology influence of French pente "slope," and English house (the meaning at that time was "attached building with a sloping roof or awning"). Originally a simple structure (Middle English homilies describe the stable where Jesus was born as a "penthouse"); meaning "apartment or small house built on the roof of a skyscraper" is attested by 1921, from which time dates its association with luxury.

Old English to, ta, te, "in the direction of, as far as (a place, state, goal)," opposite of from; also "for the purpose of, furthermore;" from West Germanic *to (source also of Old Saxon and Old Frisian to, Dutch toe, Old High German zuo, German zu "to"). Not found in Scandinavian, where the equivalent of till (prep.) is used.

This is reconstructed to be from PIE pronominal base *do- "to, toward, upward" (source also of Latin donec "as long as," Old Church Slavonic do "as far as, to," Greek suffix -dē "to, toward," Old Irish do, Lithuanian da-), from demonstrative *de-. Also see too.

English to also supplies the place of the dative in other languages. The near-universal use of to as the verbal particle with infinitives (to sleep, to dream, etc.) arose in Middle English out of the Old English dative use of to and helped shade out the Old English inflectional endings. In this use to is a mere sign, without meaning. Compare similar use of German zu, French à, de.

As an adverb of motion, direction, etc., "to a place in view, to a thing to be done," in Old English. This use was frequent in Middle English in verbal combinations where it renders Latin ad-, com-, con-, ex-, in-, ob-. As a conjunction, "until, up to the time that," by late Old English.

The distribution of verbs among at, to, with, of has been idiosyncratic and varied. Before vowels it was sometimes shortened to t'. The phrase what's it to you "how does that concern you?" (1819) is a modern form of an old question:

Huæd is ðec ðæs?

[John xxi:22, in Lindisfarne Gospel, c.950]

Used absolutely at the end of a clause. with ellipsis of infinitive (same as the proceeding clause: would do it but don't have time to), it is attested from 14c.; OED reports it "rare before 19th c.; now a frequent colloquialism."