- Multiply suggests increase in number, specif. by procreation rabbits multiply rapidly
- Augment , a more formal word, generally implies increase by addition, often of something that is already of a considerable size, amount, etc. to augment one's income
- Enlarge specifically implies a making or becoming greater in size, volume, extent, etc. to enlarge a house, a business, etc.
- Increase , the general word in this list, means to make or become greater in size, amount, degree, etc. to increase one's weight, one's power, debts, etc.