OK. After clearing through the initial tutorial puzzles to get to Area 1, the Ruins, what you need to access the final level (in which you get this achievement) is three flowers. You get flowers by collecting the required number of dandelions (puzzles clear) in each of three areas. Each time you get a flower you also open the next area(s). You'll need:
8 from Area 1, the Lake,
8 from Area 2, the Solitary Island,
and then you have your choice of
6 from area 3, the Temple Ruins, or
7 from area 4, the Forest of Fall.
Since you may opt to do some puzzles and not others in these areas, I will leave the puzzle solutions to whoever writes up guides for the "complete all puzzles in (area)" achievements.
Once you have your 3 flowers, a new stage opens on the world Map to the south of the Lake. It is entitled "A WAY OUT?".
There are two solutions to this puzzle. To get the achievement, you need to satisfy not the "win" condition, but the "end" condition. This will turn all words into flowers. Collect all the flowers and view the end cutscene.
FINAL PUZZLE SOLUTION below.
*** Spoiler - click to reveal ***
A lot of this area is here to troll you. You can disable "belt is shift" for example, but it doesn't help. You'll probably notice the nearness of "win" to "flag is", and also that "end" is down in that area as well. It's blocked by a rock though, so there's your hint if you want to work out the rest yourself.
OK, we need Rock is Push. First push Rock three steps down so it's more accessible for sentence-forming. Now, you'll notice Ice is Melt and Ice has Wall and Baba is Hot. This means the ice tiles on the right are good for one traversal only. You can however push "is" up there without stepping on them yourself.
Maneuver "is" (from "keke is push") to the left ice tile, and no further. Then use "box" (or "keke") to push "is" through without melting the ice. Go through the RIGHT ice tile, and push "is" up against "rock", then push "rock is" two tiles left. Baba should be directly below the conveyer belt. Exit via the left ice tile to get the word back out (I am not sure you have to do it this way, but this works).
Now you can manuever "push" onto the conveyer belt, and follow it, pushing it down to form "rock is push". You can clear the stage here by pushing the rocks to make "flag is win" and going to the flag, but that doesn't get you the achievement. Instead, you need flag is end.
Since you can't avoid "skull is defeat" to get to "end", you need to make skull something else. "box" or "keke" will do nicely -- push them left into the top-left rock and keep pushing until "skull is [box/keke]" (it doesn't matter which). Now there are no skulls, so you can push end over and... oh, it won't fit under "flag is"? No problem, push "rock is" to the right to make "rock is weak", and now you can push one more tile and break the rock.
Go to the flag, collect all the flowers, cheevo get, roll credits.