In my world, M reminds me of Mathematics. Last year's book is dying.

M is for Milly, my daughter's dog.
M is for mummy, when studying Egypt.
M is for homemade marshmallows!
M is for mullien, which we studied in our nature study.
And M is for music. This month's composer is Giuseppi Verdi. Here is "Triumphal March" (Grand March) from Aida:
What does the letter "M" make YOU think of?