Make the most of
To make the most of something is to use it to the best advantage.
- He made the most of his foreign holiday by visiting as many places as he could.
Make a move
To make a move is to take action.
Mow someone down
To mow someone down is to kill them by gunfire or by knocking them down with a car.
- The old woman was mowed down by a truck.
Muck something up
To muck something up is to spoil something.
Muck about / around
To muck about is to behave in a silly way.
Mull something over
To mull something over is to think about something at length.
Mum’s the word
An expression used to mean that you will not reveal a secret.
If something passes muster, it is accepted as satisfactory.