For example, if I said, I promise I will do something. Is there a word for me? Promise giver?
Is there a one word noun for this?
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Promiser seems to be a valid word:
Noun 1. promiser - a person who makes a promise
Additionally, the word promisor means the same thing in a legal context:
PROMISOR. One who makes a promise.
a pledger seems to be what you're after:
Example from http://www.oxforddictionaries.com/definition/english/pledge :
‘Even so, the local authority would be aware of the statistics of the American programme, from whence they get their inspiration, and its 88 per cent failure rate amongst pledgers.’
You could say that if you are a promise-giver you are avowed.
(As the avower you are sworn)
Another possibility is guarantor.