In English, of rules, discipline, etc., from mid-15c. Related: Laxly; laxness. A transposed Vulgar Latin form yielded Old French lasche, French lâche. The laxists, though they formed no avowed school, were nonetheless condemned by Innocent XI in 1679.
late 14c., of persons, "self-indulgent, loving ease;" also "sensitive, easily hurt, feeble;" of things, "delightful," from Latin delicatus "alluring, delightful, dainty," also "addicted to pleasure, luxurious, effeminate," in Medieval Latin "fine, slender;" related to deliciae "pleasure, delight, luxury," and delicere "to allure, entice," from de "away" (see de-) + lacere "to lure, entice," which is of uncertain origin. Compare delicious, delectable, delight.
Meaning "so fine or tender as to be easily broken" is recorded from 1560s. Meaning "requiring nice and skillful handling" is by 1742. Sense of "exquisitely adjusted in construction" is from 1756. Related: Delicateness.
Sense of "leniency, forbearance of restraint or control of another, gratification of desire or humor" is attested from late 14c. That of "yielding to one's inclinations" (technically self-indulgence) in English is from 1630s. In British history, Indulgence also refers to grants of certain liberties to Nonconformists under Charles II and James II, as special favors rather than legal rights. The sale of indulgences in the original Church sense was done at times merely to raise money and was widely considered corrupt; the one in 1517 helped to spark the Protestant revolt in Germany.
From c. 1200 of material things, "not stiff, not coarse, fine; yielding to weight." From late 14c. of wind, rain, etc. Of sounds, "quiet, not loud," from early 13c. Of words, "mild, restrained; courteous" mid-14c. From late 14c. as "indulgent," also "physically feeble; easily overcome, lacking manly courage." From 1755 of water ("relatively free from mineral salts"), from 1789 of coal. Meaning "foolish, simple, silly" is attested from 1620s; earlier "easily moved or swayed; soft-hearted, sympathetic; docile" (early 13c.). In reference to drinks, "non-alcoholic" from 1880. As an adverb, Old English softe "gently;" late 13c. as "quietly." As an interjection from 1540s.
Soft landing is from 1958 and the U.S. space program. Adjective soft-core (in reference to pornography) is from 1966 (see hardcore). Soft rock as a music style is attested from 1969. Soft sell is from 1955. Soft-shoe as a dancing style is attested from 1927. Soft-boiled is from 1757 of eggs; of persons, ideas, etc., 1930 (compare half-baked). Soft-focus (adj.) of camera shots is from 1917. The softer sex "women collectively" is from 1640s.