Weather & Environment:
* Mistletoe
* Mizzle (light rain)
* Mists
* Mountain
* Mud (from melting snow)
Clothing & Activities:
* Mittens
* Muffler (scarf)
* Monotony (of a long winter)
* Melting (of snow and ice)
* Memories (of winter holidays)
Other:
* Magical (for winter's beauty)
* Merry (for the holidays)
* Month (December)
* Midnight (short days)
* Moment (of winter peace)
Let me know if you'd like more!