1640s, "continue to advance," also "manage, be engaged in," from carry (v.) + on (adv.). The meaning "conduct oneself in a wild and thoughtless manner" is by 1828. Carryings-on is from 1660s as "questionable doings," from 1866 as "riotous behavior." As an adjective, carry-on, in reference to luggage that may be brought into the passenger compartment of an airliner, is attested by 1965.
1680s; see April + fool (n.). April-gowk (from Old Norse gaukr "a cuckoo") is a northern variant. April Fool's Day customs of sending people on false errands seem to have come to England from France late 17c.; originally All Fool's Day (1712). In Cumberland, Westmorland and northern parts of Lancashire and Yorkshire, however, May 1 was the day for hoaxing, and the fool was a May gosling. That custom is attested by 1791.
1710, "from cause to effect," a Latin term in logic from c. 1300, in reference to reasoning from antecedent to consequent, based on causes and first principles, literally "from what comes first," from priori, ablative of prior "first" (see prior (adj.)). Opposed to a posteriori. Since c. 1840, based on Kant, used more loosely for "cognitions which, though they may come to us in experience, have their origin in the nature of the mind, and are independent of experience" [Century Dictionary]. Related: Apriorist; apriorism; aprioristic. The a is the usual form of Latin ab "off, of, away from" before consonants (see ab-).
legal Latin, "in the process of being done," from fieri "to come into being, become," used as passive of facere "to make, do" (from PIE root *dhe- "to set, put").
writ concerning a sum awarded in judgment (often requiring seizure and sale of property for debt), Latin, literally "cause it to be done, cause to be made," the first words of the writ, from Latin fieri "to be made, come into being" (see fiat). Second word from facere "to do" (from PIE root *dhe- "to set, put").
day set aside in U.S. "for planting forest trees to make lumber for the generations yet to come" ["Congressional Record," June 1892], first celebrated April 10, 1872, in Nebraska (a largely treeless state), the brainchild of U.S. agriculturalist and journalist J. Sterling Morton (1832-1902). From Latin arbor, arboris "tree" (see arbor (n.2)).