snoop v.

1520s, of animals, "make a quick bite" (intransitive), from or cognate with Dutch or Low German snappen "to snap," which could be related to Middle Low German or Middle Dutch snavel "bill, beak," which Watkins traces to a hypothetical Germanic root *snu- forming words having to do with the nose, imitative of a sudden drawing of breath (see snout). Ultimately imitative. Compare earlier gnappen "snap with the teeth" (c. 1300).

The intransitive meaning "break suddenly or sharply" is from c. 1600. The transitive sense of "take or catch unexpectedly with a bite" is from 1560s; that of "shut with a sharp sound" is from 1570s.

The meaning "come or move into place with a snap" is attested from 1793. In a broader sense of "do (something) hastily or eagerly" it is attested by 1798. The meaning "take an instant photograph" is from 1890. The U.S. football sense is by 1887 (see the noun).

To snap at "speak sharply or harshly to" is from 1570s. To snap in the mental sense of "suddenly lose control, composure, or sanity" is from 1970s. Related: Snapped; snapping.

In reference to the noise made with the fingers and palm, from 1670s (snap with one's fingers). The phrase snap out of it "change one's behavior suddenly" is recorded by 1907. The snapping turtle, large, ferocious freshwater turtle of the U.S., is so called by 1784, for its powerful bite. Snap-brim (adj.) in reference to a type of hat is from 1928.

early 13c., "trunk or projecting nose of an animal, the nose or jaws when protrusive," not found in Old English, from Middle Low German and Middle Dutch snute "snout," from Proto-Germanic *snut- (source also of German Schnauze, Norwegian snut, Danish snude "snout").

Throughout the Germanic languages a group of words in sn- (Modern German and Yiddish schn-) relate to the human nose or the animal snout. Probably the root is imitative. The senses can extend to the snap of a dog's snout; the snort a horse can make, and the rough or obstructed breathing of a human snore. Also compare snarl, sneeze, snooze, snuff, snoop, snot, etc. Their relation to another Germanic group having to do with "to cut; a detached part" (snip, snick, etc.) is uncertain, but the senses tend to overlap.

Of other animals and (contemptuously) of humans from c. 1300. 16c.-17c. English had snout-fair "good-looking" (1520s).

Lady Strangelove: Not as a suitor to me sir?

Mr. Swaynwit: No you are too great for me. Nor your Mopsey without, though shee be snout-faire, and has some wit shee's too little for me ...

[Brome, "The Court Beggar," 1632]

"inquisitive, excessively prying," by 1895, from snoop (n.) + -y (2). The cartoon dog of that name is from the syndicated newspaper comic strip that came to be called "Peanuts," in which he debuted for a national audience on Oct. 4, 1950.