Yes, FINEST is a Scrabble word!

Letter values in Scrabble US: F 4, I 1, N 1, E 1, S 1, T 1.

Is it a valid word?

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

being satisfactory or in satisfactory condition
minutely precise especially in differences in meaning
thin in thickness or diameter
characterized by elegance or refinement or accomplishment
of textures that are smooth to the touch or substances consisting of relatively small particles
free from impurities; having a high or specified degree of purity

Also: all right, o.k., hunky-dory.