Yes, SQUILL is a Scrabble word!

Letter values in Scrabble US: S 1, Q 10, U 1, I 1, L 1, L 1.

Is it a valid word?

SQUILL is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

bulb of the sea squill, which is sliced, dried, and used as an expectorant
having dense spikes of small white flowers and yielding a bulb with medicinal properties
an Old World plant of the genus Scilla having narrow basal leaves and pink or blue or white racemose flowers

Also: sea squill, sea onion, urginea maritima.