What's the "een" in Halloween?
late 14c., "hollow at the base of the throat above the breastbone," from Old French esclot "hoofprint of a deer or horse," of uncertain origin, probably from Old Norse sloð "trail" (see sleuth). Original sense is rare or obsolete in Modern English; sense of "narrow opening into which something else can be fitted" is first recorded 1520s. Meaning "middle of the (semi-circular) copy desk at a newspaper," the spot occupied by the chief sub-editor, is recorded from 1917. The sense of "opening in a machine for a coin to be inserted" is from 1888 (slot machine first attested 1891). The sense of "position in a list" is first recorded 1942; verb sense of "designate, appoint" is from 1960s. Slot car first attested 1966.
"bar or bolt used to fasten a door, window, etc.," c.1300, from Middle Dutch or Middle Low German slot (cf. Old Norse slot, Old High German sloz, German Schloss "bolt, bar, lock, castle;" Old Saxon slutil "key," Dutch slot "a bolt, lock, castle"), from Proto-Germanic stem *slut- "to close" (cf. Old Frisian sluta, Dutch sluiten, Old High German sliozan, German schliessen "to shut, close, bolt, lock"), from PIE root *klau- "hook, peg" (cf. Greek kleis "key;" Latin claudere "to shut, close," clavis "key," clavus "nail;" see close (v.)). Wooden pegs seem to have been the original keys.
1747, "provide with a slot, cut slots in," from slot (n.1). Meaning "drop a coin in a slot" is from 1888. Sense of "take a position in a slot" is from 1940; that of "fit (something) into a slot" is from 1966. Oldest sense is obsolete: "stab in the base of the throat" (c.1400). Related: Slotted; slotting.
1560s, "to bolt a door," from slot (n.2). Related: Slotted; slotting.
A slot machine; one-arm bandit: The slots are going day and night (1950+)