Pronounced as it is spelled.
1. Noun. A term used for anything that is added to give more effect or power.
Example: This sauce needs a little more oomf.
2. Synonym in certain situations: potency, power, effectiveness, kick (slang).
Example: Let's give a little more oomf to this drink.
NOTE: This word is often used by older people when they think they're being adventurous in things like cooking. They cannot think of any exciting words so they say 'oomf'. It is rather difficult to string casually within a sentence because of the way it is pronounced, and therefore the speaker will surround the word with a pause and incidentally add emphasis to the word. Then it comes off as almost flamboyant.
Most common usages of the word occur within the subject of food. In this case, a close synonym is 'spice' in making something 'spicy'.
For very creepy results, use this word to describe a person.
Example: You've got a lot of oomf to you, now don't you?
In the above case, a synonym would be 'zest'.
But generally, this word is only used for food.