Yes, CASTES is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, S 1, T 1, E 1, S 1.

Is it a valid word?

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

social status or position conferred by a system based on class
(Hinduism) a hereditary social class among Hindus; stratified according to ritual purity
a social class separated from others by distinctions of hereditary rank or profession or wealth
in some social insects (such as ants) a physically distinct individual or group of individuals specialized to perform certain functions in the colony

put or send forth
deposit
select to play,sing, or dance a part in a play, movie, musical, opera, or ballet
throw forcefully
assign the roles of (a movie or a play) to actors
move about aimlessly or without any destination, often in search of food or employment
form by pouring (e.g., wax or hot metal) into a cast or mold
get rid of
choose at random
formulate in a particular style or language
eject the contents of the stomach through the mouth

Also: cast off, shake off, throw off, throw away, vomit up, be sick, throw up.