Yes, triple is a Scrabble word!

Verb

1. Increase threefold

2. Hit a three-base hit

Adjective

1. Having three units or components or elements

2. Three times as great or many

Noun

1. A base hit at which the batter stops safely at third base

2. A set of three similar things considered as a unit

3. A quantity that is three times as great as another