Entries linking to water-moccasin
Old English wæter, from Proto-Germanic *watr- (source also of Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, German Wasser, Old Norse vatn, Gothic wato "water"), from PIE *wod-or, suffixed form of root *wed- (1) "water; wet."
To keep (one's) head above water in the figurative sense is recorded from 1742. Water cooler is recorded from 1846; water polo from 1884; water torture from 1928. Linguists believe PIE had two root words for water: *ap- and *wed-. The first (preserved in Sanskrit apah as well as Punjab and julep) was "animate," referring to water as a living force; the latter referred to it as an inanimate substance. The same probably was true of fire (n.).
1610s, foot-covering worn originally by native North American people (made of deerskin or soft leather and without a stiff sole), from an Algonquian language of Virginia, probably Powhatan makasin "shoe," from Central Atlantic Coast Algonquian *mockasin, which is similar to Southern New England Algonquian *makkusin, Munsee Delaware mahkusin, Ojibwa makizin. Related: Moccasined.
As a name for a type of venomous snake of the southern U.S. (1784), it is perhaps a different word, but none has been found to match it. Bright regards them as identical, but the sense connection is difficult to explain.