Determine the difficulty of an english word

Question

I am working a word based game. My word database contains around 10,000 english words (sorted alphabetically). I am planning to have 5 difficulty levels in the game. Level 1

Answer 1

Crowd-source the answer.

• Create an online 'game' that lists 10 words at random.
• Get the player to drag and drop them into easiest - hardest, and tick to indicate if the player has ever heard of the word.
• Apply an ranking algorithm (e.g. ELO) on the result of each experiment.
• Repeat.

It might even be fun to play, you could get a language proficiency score at the end.