Nice! You definitely have something there.
I would love a dictionary lookup. I'd expect a big part of the strategy to be working backwards from the possible 1/2 letter words, but there's no way to tell how reasonable the dictionary is without testing, and getting the game into the proper state to test would be just as hard as solving the puzzle in the first place.
Having two separate goals (eliminate all letters, find all the words) seems confusing. Honestly I find the latter to be a fairly tedious prospect, but the game really seems to push you toward it especially with the colors on the calendar depending on the % of words found. "Damn it, I got a perfect score with no undos, and all I have to show for it is a red square showing how bad a job I did!"
The UI (on a desktop) felt kind of broken at the start because nothing has hover effects. Anything clickable would benefit from some kind of an effect, but especially the letters on the words. If you don't want color changes or animations, at least set the cursor style.
Thank you so much for the feedback! The dictionary look up feature is a great idea-- I had never thought of it before, but it does solve a pain point with the game you've articulated well.
The desktop UI suggestions are also very helpful. I've updated the desktop version with some minor hover effects and cursor styling. I've mostly been focused on mobile, so it was good hear some feedback for desktop.