This achievement is not that hard, provided you have two controllers. First, start a 'local' game, with the profile getting the achievement, and some other profile on controller number 2. Play an 'original' game. It does not matter whom goes first. Have the other player discard tiles until they get the letters 'TENT', while you continually discard tiles to get 'ATIVE'. Have the second player place 'TENT' on the center, but (this is important) the LAST T being the center (the letter that goes on the diamond space). The profile that is getting the achievement, places 'ATIVE' behind this, to make 'TENTATIVE'.
Voila. Now, the worst part is, you actually have to FINISH the game. But consider that you can discard tiles, pass turns, etc, and it should finish eventually.
If you are trying to get 'A Column of 7' achievement as well, then make sure the 'TENT' player places the word vertically, with room on the bottom to place 'ATIVE'.