1856, "full of loops," from loop (n.) + -y (2). Slang sense "crazy" is attested from 1923. The earlier figurative sense was "crafty, deceitful" (1824), popularized by Scott's novels.
Entries linking to loopy
loop n.
late 14c., "a fold or doubling of cloth, rope, leather, cord, etc.," of uncertain origin. OED favors a Celtic origin (compare Gaelic lub "bend," Irish lubiam), which in English was perhaps influenced by or blended with Old Norse hlaup "a leap, run" (see leap (v.)). As a feature of a fingerprint, 1880. In reference to magnetic recording tape or film, first recorded 1931. Computer programming sense "sequence of instructions executed repeatedly" first attested 1947.
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.