Yes, COWSLIP is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, W 4, S 1, L 1, I 1, P 3.

Is it a valid word?

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

early spring flower common in British isles having fragrant yellow or sometimes purple flowers
swamp plant of Europe and North America having bright yellow flowers resembling buttercups

Also: primula veris, marsh marigold, meadow bright, may blob, water dragon, caltha palustris.

Not playable in Scrabble US: PAIGLE.