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hairy hair·y (hâr'ē)
adj. hair·i·er, hair·i·est
Covered with hair or hairlike projections.
Consisting of or resembling hair.
[last sense probably fr the hairy monsters of horror films, but the sense of ''difficult'' was used at 19th-century Oxford, and that of ''dangerous'' in the British armed forces of the 1930s]
1. Annoyingly complicated. "DWIM is incredibly hairy."
2. Incomprehensible. "DWIM is incredibly hairy."
3. Of people, high-powered, authoritative, rare, expert, and/or incomprehensible. Hard to explain except in context: "He knows this hairy lawyer who says there's nothing to worry about." See also hirsute.
The adjective "long-haired" is well-attested to have been in slang use among scientists and engineers during the early 1950s; it was equivalent to modern "hairy" and was very likely ancestral to the hackish use. In fact the noun "long-hair" was at the time used to describe a hairy person. Both senses probably passed out of use when long hair was adopted as a signature trait by the 1960s counterculture, leaving hackish "hairy" as a sort of stunted mutant relic.