noun

• (Germanic mythology) A supernatural being or spirit associated with illness, mischief, and harmful or dangerous magical influence; in later Norse sources, sometimes divided into benevolent light elves (inhabiting Álfheimr) and malevolent dark elves.
  "[…] if theyr children at any time vvere frowarde and vvanton, they would ſay to them that the Guelfe or the Gibeline came. VVhich vvords novve from them (as many thinge els) be come into our vſage, and for Guelfes and Gibelines, we ſay Elfes & Goblins."
• (folklore) A small, magical creature similar to a fairy, often mischievous, playful, or occasionally helpful.
  "For there and ſeveral other places / About mill dams and green brae faces, / Both Elrich, Elfs and Brownies ſtayed, / And Green gown’d Farries daunc’d and played; […]"
• (fantasy) A member of a race of tall, slender, graceful beings with pointed ears, typically immortal or very long-lived and possessing wisdom and magical abilities.
  "He was not speaking troll-talk now, but the language of Elfland, that grander tongue that he had had to speak when he was before the King: for he knew the language of Elfland although it was never used in the homes of the trolls, who preferred troll-talk. This language was spoken in those days also by men, for there were fewer languages then, and the elves and the people of Erl both used the same."
• (obsolete) A very diminutive person; a dwarf.

verb

• (now rare) To twist into elflocks (of hair); to mat.
  "My face I'll grime with filth, blanket my loins, elf all my hairs in knots, and with presented nakedness outface the winds and persecutions of the sky."

noun

• (file format) Acronym of Executable and Linking Format, a common object file format for Unix.
  "In ELF executables, there aren't a whole lot of code caves (such as in the PE format), so you are not likely to be able to shove more than just a meager amount of shellcode into existing code slots […]"
• (electronics) Initialism of extremely low frequency.
• (linguistics) Acronym of English as a Lingua Franca (“English used by non-native speakers”).
  "The consequences of the massive volume of ELF to English taken as a whole, as the aggregate use of the language, is essentially a descriptive issue: what new features of English are emerging and taking hold?"