"vessel used for holding liquids," late 14c., from Medieval Latin phiola, from Latin phiala, from Greek phialē "flat vessel, dish, flat bowl for drinking or sacrificing," a loan-word of unknown origin. It also came to Middle English via Old French fiole "flask, phial" (12c.), hence the diversity of Middle English spellings (fiole,phiole,phial,fial,viole,vial,viele) and modern vial.
1540s, "person who boils," agent noun from boil (v.). The meaning "vessel for boiling" is from 1725; the specific sense of "strong metallic structure in which steam is generated for driving engines" is from 1757.
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.
1758, "sleeping-berth in a vessel," later in a railway car, etc., probably a shortened form of bunker (n.) in its sense of "seat." Bunk-bed (n.) attested by 1869.
late 14c., "large tub-like vessel," corresponding to Middle Dutch tanckaert, meaning the same thing, but both of unknown origin. A guess hazarded in OED is that it is a transposition of *kantard, from Latin cantharus. Klein suggests French tant quart "as much as a quarter." "The notion that the word is from tank 1 + -ard is wholly untenable" [Century Dictionary]. Meaning "drinking vessel" is first recorded late 15c.