Yes, whistle is a Scrabble word!

Verb

1. Make whistling sounds

2. Move with, or as with, a whistling sound

3. Utter or express by whistling

4. Move, send, or bring as if by whistling

5. Make a whining, ringing, or whistling sound

6. Give a signal by whistling

Noun

1. The sound made by something moving rapidly or by steam coming out of a small aperture

2. The act of signalling (e.g., summoning) by whistling or blowing a whistle

3. A small wind instrument that produces a whistling sound by blowing into it

4. Acoustic device that forces air or steam against an edge or into a cavity and so produces a loud shrill sound

5. An inexpensive fipple flute