Yes, trill is a Scrabble word!

Verb

1. Pronounce with a trill, of the phoneme `r'

2. Sing or play with trills, alternating with the half note above or below

Noun

1. A note that alternates rapidly with another note a semitone above it

2. The articulation of a consonant (especially the consonant `r') with a rapid flutter of the tongue against the palate or uvula