elfin

Etymology 1

From Middle English elven, from Old English elfen, ælfen (“nymph, spirit, fairy”), feminine of elf, ælf (“elf”), equivalent to elf + -in. Cognate with Middle High German elbinne (“a fairy, nymph”).

noun

1. An elf; an inhabitant of fairy-land.
2. A little urchin or child.
3. Any of the butterflies in the subgenus Incisalia of the North American lycaenid genus Callophrys.

Etymology 2

Partly from attributive use of Etymology 1, but reanalysed by Spenser as if equivalent to elf + -in. Compare elven (adj), elvan.

adj

1. Relating to or resembling an elf or elves, especially in its tiny size or features.
   He’s forced to travel back to 1969 to prevent an evil alien (a shockingly effective, nearly unrecognizable Jemaine Clement of Flight Of The Conchords, playing sort of a psychotic extraterrestrial-biker serial killer) from destroying the world by killing Brolin. Smith is aided in his quest by an elfin, time-jumping alien with psychic powers played by another Coen brothers veteran, A Serious Man star Michael Stuhlbarg. May 24, 2012, Nathan Rabin, “Film: Reviews: Men In Black 3”, in The Onion AV Club