Weird is a wayward word: though it describes a set of singular effects that link the cultural fringe with peculiar personal experiences, it remains an elusive and marginal term. The similar notion of the uncanny is, on the other hand, basically an establishment term, a well-established literary effect with a sophisticated psychoanalytic pedigree. Weirdness, we might say then, is the uncanny's low-brow doppelganger, a demotic country cousin that races hot-rods, wears mis-matched socks, and inhabits the strange borderlands between this world and the beyond.
The roots of weirdness lie in the noun wyrd, an Old English term that pops up in Beowulf and denotes the (usually grim) demands of destiny. The adjective first appears in the phrase weird sisters, which was used by Scottish poets to describe the classical Fates before Shakespeare attached the term to the witches of Macbeth. But Shakespeare's spelling of weird is, well, a bit weird—"weyrd", "weyward", and "weyard" appear in the first folio, but never "weird". These alternate spellings, again, suggest the term wayward, a word used by Shakespeare to denote the capricious refusal to follow rule or reason. This suggests to some Macbeth scholars that, in addition to their oracular knowledge, the witches are also defined by their willful resistance to the norm, a perverse and chaotic twist away from the law. Early on, then, weirdness already covers two contrasting but related forces: necessity and anomaly.