The longest possible word is RADIOSONDE, which is ten letters long and is a unit of measurement for weather balloons. There's no word that can be made with all of those letters.
No single word can be made with the letters: "i d e l o x."
forehead
hared, heard
In English the largest word you can make is woaded, which uses six of the seven letters. There are no valid seven-letter combinations from the pattern a d d e h o w.
Daydream.
Sized
No single word can be made with the letters: "i d e l o x."
relieved
forehead
centrifuge
hared, heard
The longest word you can make with these letters is jeeped.
In English the largest word you can make is woaded, which uses six of the seven letters. There are no valid seven-letter combinations from the pattern a d d e h o w.
Daydream.
knithreaded
diegest
homestead