"to touch down," as a bird from flight, "get down or descend," as a person from horseback, from Old English lihtan "to alight; to alleviate, make less heavy," from Proto-Germanic *linkhtijan, literally "to make light," from *lingkhtaz "not heavy" (see light (adj.1)). Apparently the etymological sense is "to dismount" (a horse, etc.), and thus relieve it of one's weight."
Alight has become the more usual word. To light on "happen upon, come upon" is from late 15c. To light out "leave hastily, decamp" is 1866, from a nautical meaning "move out, move heavy objects" (1841), a word of unknown origin but perhaps belonging to this word (compare lighter (n.1)).
It forms all or part of: alleviate; alleviation; alto-rilievo; carnival; elevate; elevation; elevator; leaven; legerdemain; leprechaun; Levant; levator; levee; lever; levity; levy (v.) "to raise or collect;" light (adj.1) "not heavy, having little weight;" lighter (n.1) "type of barge used in unloading;" lung; relevance; relevant; releve; relief; relieve.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit laghuh "quick, small;" Greek elakhys "small," elaphros "light;" Latin levare "to raise," levis "light in weight, not heavy;" Old Church Slavonic liguku, Russian lëgkij, Polish lekki, Lithuanian lengvas "light in weight;" Old Irish lu "small," laigiu "smaller, worse;" Gothic leihts, Old English leoht "not heavy, light in weight."
"dining hall," especially in a monastery, early 15c., refectori, from Medieval Latin refectorium, "place of refreshment," from past participle stem of reficere "to remake, restore," from re- (see re-) + combining form of facere "to make, do" (from PIE root *dhe- "to set, put").
Middle English (and after) also had it as a verb, refeten, "to refresh, restore, feed" (late 14c.), from Anglo-French refeter, Old French refactier. Also refection "refreshment, nourishment," all ultimately from Latin. Some survive in specialized senses.
For after a draught of wine, a Man may seem lighter in himself from sudden refection, although he be heavier in the balance, from a corporal and ponderous addition; but a Man in the morning is lighter in the scale, because in sleep some pounds have perspired; and is also lighter unto himself, because he is refected. [Browne, "Vulgar Errors," iv. 7]
c. 1400, "delightful to one of the senses, highly pleasing," from Old French delectable delitable and directly from Latin delectabilis "delightful," from delectare "to allure, delight, charm, please," frequentative of delicere "entice" (see delicious). The earlier form in English was delitable (late 13c.). Since c. 1700 "rarer, more or less affected or humorous, and restricted to the lighter kinds of pleasure" [OED]. Related: Delectably.