Hal·low·een also Hal·low·e'en 
(hăl′ə-wēn, hŏl′-)
(hăl′ə-wēn, hŏl′-)n.
October 31, celebrated in the United States, Canada, and the British Isles by children going door to door while wearing costumes and asking for treats and playing pranks.
[Short for All Hallow Even : ALLHALLOW(MAS) + EVEN2.]