lax (adj.) Look up lax at
c. 1400, "loose" (in reference to bowels), from Latin laxus "wide, spacious, roomy," figuratively "loose, free, wide" (also used of indulgent rule and low prices), from PIE *lag-so-, suffixed form of root *(s)lēg- "to be slack, be languid" (source also of Greek legein "to leave off, stop," lagos "hare," literally "with drooping ears," lagnos "lustful, lascivious," lagaros "slack, hollow, shrunken;" Latin languere "to be faint, weary," languidis "faint, weak, dull, sluggish, languid").

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.
lax (n.) Look up lax at
"salmon," from Old English leax (see lox). Cognate with Middle Dutch lacks, German Lachs, Danish laks, etc.; according to OED the English word was obsolete except in the north and Scotland from 17c., reintroduced in reference to Scottish or Norwegian salmon.
lax (n.) Look up lax at
1951 as an abbreviation of lacrosse.