Yes, treble is a Scrabble word!

Verb

1. Sing treble

2. Increase threefold

Adjective

1. Having or denoting a high range

2. Three times as great or many

3. Having three units or components or elements

4. Having more than one decidedly dissimilar aspects or qualities; public preaching and private influence"- R.W.Emerson

Noun

1. The pitch range of the highest female voice