The words "massive" ,"monumental", "monstrous", "measureless", "mammoth", "massy", "mastodonic", "mighty", "monster", "monstrous", "mountainous" and the slang word "mega" come to mind. However to me the word "immense" would be the best alternative.
Modernize is a word that starts with m and means to upgrade.
Make is a word that means to create and starts with "m".
The word you are looking for is "clever."
Misery
mountainous
"Matter" is a possibility.
monarch
Muscle.
The word is magnificent.
Merge
Mane?
minister