late 15c., "sodium carbonate," an alkaline substance extracted from certain ashes (now made artificially), from Italian sida (or Medieval Latin soda) "a kind of saltwort," from which soda was obtained, of uncertain origin. Perhaps it is from a Catalan sosa, attested from late 13c., of uncertain origin. Proposed Arabic sources in a name of a variety of saltwort have not been attested and that theory is no longer considered valid. Another theory, considered far-fetched in some quarters, traces it to Medieval Latin sodanum "a headache remedy," ultimately from Arabic suda "splitting headache."
Soda is found naturally in alkaline lakes, in deposits where such lakes have dried, and from ash produced by burning various seaside plants. A major trading commodity in the medieval Mediterranean, since commercial manufacture of it began in France in late 18c., these other sources have been abandoned. Washing soda (sodium carbonate) is commonly distinguished from baking soda (sodium bicarbonate). A soda-cracker (1863) has baking soda as an ingredient.
The meaning "carbonated water" is first recorded 1834, a shortening of soda water (1802) "water into which carbonic acid has been forced under pressure." "It rarely contains soda in any form; but the name originally applied when sodium carbonate was contained in it has been retained" [Century Dictionary, 1902]. Since 19c. typically flavored and sweetened with syrups. First record of soda pop is from 1863, and the most frequent modern use of the word is as a shortening of this or other terms for "flavored, sweetened soda water." Compare pop (n.1). Soda fountain is from 1824; soda jerk first attested 1915 (soda-jerker is from 1883). Colloquial pronunciation "sody" is represented in print from 1900 (U.S. Midwestern).
Old English 1st and 3rd person singular present indicative of cunnan "to know," less commonly as an auxiliary, "have power to, to be able," (also "have carnal knowledge"), from Proto-Germanic *kunnjanan "be mentally able, have learned" (source also of Old Norse kenna "become acquainted, try," Old Frisian kanna "recognize, admit, know," German kennen "know," Middle Dutch kennen "know," Gothic kannjan "make known"), from PIE root *gno- "to know."
It holds now only the third sense of "know," that of "know how to do something" (as opposed to "know as a fact" and "be acquainted with" something or someone). Also used in the sense of may, denoting mere permission. An Old English preterite-present verb, its original past participle, couth, survived only in negation (see uncouth), but compare could. The present participle has spun off with a deflected sense as cunning.
generally, "a small cylindrical sheet-metal vessel used to contain liquids, preserves, etc.," Old English canne "a cup, container," from Proto-Germanic *kanna (source also of Old Saxon, Old Norse, Swedish kanna "a can, tankard, mug," also a unit of measure, Middle Dutch kanne, Dutch kan, Old High German channa, German Kanne). Probably it is an early borrowing from Late Latin canna "container, vessel," from Latin canna "reed," also "reed pipe, small boat;" but the sense evolution is difficult.
The modern sense of "air-tight vessel of tinned iron" is from 1867. The slang meaning "toilet" is c. 1900, said to be a shortening of piss-can; the meaning "buttocks" is from c. 1910, perhaps extended from this.
"5-gallon metal container," 1943, from Jerry "a German." It was first used by German troops in World War II and later adopted by the Allies.
"confident of performance," by 1952, from expression can do "it is possible" (1903), literally "(I or we) can do (it)," which is perhaps based on earlier no can do (see no).
late 14c., "soda ash," from Medieval Latin alkali, from Arabic al-qaliy "the ashes, burnt ashes" (of saltwort, which abounds in soda due to growing in alkaline soils), from qala "to roast in a pan." Later extended to similar substances, natural or manufactured. The modern chemistry sense is from 1813.