I am on level 40. What determines a 4 letter, 5 letter, 6 letter and 7 letter word?

SteveAshbaugh

I have selected up to 6 letters to make a word but do not get credit for a 6 letter word. sometimes I don't even get credit for a 4 letter word with that many letters.

aCe

It's probably because one of the letters you are using is trapped by a vine. This means you can still create the word to free the tile but it won't count towards your achievement. The best way to check is when you hover over the letters and create the word, if its going to count then the wordcount on the left hand side will glow green as well