*meg-

The core idea of this root was:

great

It’s the origin of mega and much and many more words with the syllables magni-, magi-, major or maxi.
Here’s a little (incomplete) overview:

• magnitude
• magnify
• majestic
• major
• majority
• maximum
• Mister 
• May (the month)
• mahatma (literally “great breath, soul”)