Unknown. See dialect forms caddew, caddy, cad-bait.
Meanings
(countable, uncountable) The larva of a caddis fly. They generally live in cylindrical cases, open at each end, and covered externally with debris.
However, even during times when the river is clear, [brown drakes'] presence is overshadowed by the overwhelming waves of caddis that are on the water and emerging at the same time. 2013, Boots Allen, Snake River Flies: Eighty Years of Proven Patterns for a ...:
From Middle French cadis, from Old French cadaz, from Old Occitan, from Old Catalan cadirs, cadins.
Meanings
(countable, uncountable) A rough woolen cloth; caddice.
(countable, uncountable) A kind of worsted lace or ribbon.
Hee hath Ribbons of all the colours i’ th Rainebow; Points, more then all the Lawyers in Bohemia, can learnedly handle, though they come to him by th’ grosse: Inckles, Caddysses, Cambrickes, Lawnes: c. 1610–1611 (date written), William Shakespeare, “The Winters Tale”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act IV, scene iv], page 293: