This is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles.
If a word conforms to a special rule, I call it a X-Mas Word™.
Use the following examples to find the rule.
Here is a CSV version:
X-MAS WORDS™, NOT X-MAS WORDS™
WHISKEY*, RUM
CHRISTMAS, HANUKKAH
HAPPY*, SAD
JOY, FUN
CHOCOLATE*, COCOA
YOGHURT*, MILK
IDIOT*, DUMB
GLAMOUR, FLAIR
BABY*, CHILD
EXOTIC*, PLAIN
WINTER*, SPRING
SNOWBOARDING*, SWIMMING
LIGHT, DARK
FOOD*, DRINK
JINGLE*, MUSIC
SANTA CLAUS, MICKEY MOUSE
TOY, BALL
HEAT*, CHILL
SNOW, SEA
FAILURE, SUCCESS
DROP, DRIP
DEER*, MOOSE
*Extra X-Mas Word™
The puzzle relies on the series' inbuilt assumption, that each word can be tested for whether it is a X-Mas Word™ without relying on the other words.
These are not the only examples of X-Mas Words™, many more exist and can be found.