Here is the full list of all 10 Wordament achievements worth 50 gamerscore. It takes around 1-2 hours to unlock all of the achievements on iOS.
Completed 10 rounds
You used rotate to find more words
You found a digram word
You found a theme word
You placed better than 50% of the players in a round
Found the longest possible word in a round
You played a game where you used all 16 tiles to make words
Beat all your Frenemies in a round
Play Wordament in more than one language
Complete 100 rounds