Yes, pledge is a Scrabble word!

Verb

1. Promise solemnly and formally

2. Pay (an amount of money) as a contribution to a charity or service, especially at regular intervals

3. Propose a toast to

4. Give as a guarantee

5. Bind or secure by a pledge

Noun

1. A deposit of personal property as security for a debt

2. Someone accepted for membership but not yet fully admitted to the group

3. A drink in honor of or to the health of a person or event

4. A binding commitment to do or give or refrain from something