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
4. <topology> hairy ball.
hack value « ha ha only serious « hair « hairy
» hairy ball » HAKMEM » hakspek