No, it is not. Words with Friends uses the Enhanced North American Benchmark dictionary, which does not include "OST" as a word. Scrabbles uses the SOWPODS dictionary, and similarly does not count "OST" as a word, though "SOT" is. You can use free word unscramblers like wordunscrambler.co to enter your own letters and see what counts for each game.
OST Official Sound Track
cost host lost most post
quix is an acceptable dictionary word for games like scrabble, words with friends, crossword, etc
There are 2 blanks In words with friends
There are 5 S's in Words With Friends. (The prior answer noted that there were 5 S's also in Scrabble. This is incorrect. In Scrabble, there are only 4 S's; Words With Friends features an additional S in its letter distribution.)
It is an obsolete form of "host". It is not a Scrabble word.
there are 0 c in the word friends.
these are not real words >:( poo u
In Sindarin, the word for castle or fortress is ost.
yes
East = Ost East = Osten
The number of sites that contain the word friends is actually uncountable.
OST Official Sound Track
cost host lost most post
Nord-Ost was created in 2001.
Saint-Ost's population is 81.
Ober Ost ended in 1919.