Having the characteristics, feelings, or atmosphere of Christmas; festive and suggestive of the Christmas season.
From Christmas plus the English adjectival suffix -y (from Old English -ig). This informal adjective lets speakers describe things that feel Christmas-like without formal language.
Words ending in '-y' are some of English's most playful informal formations—'christmasy' is the perfect example of how we informally describe seasonal feelings that can't be pinned down more precisely.
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