A 'complete' word is a word in which every letter, in turn, can be replaced by another to form a new word.
For example, RUG is a complete word because:
-ug = hug
r-g = rig
ru- = run
How many of the following words are not complete words? Proper nouns and names are not allowed.
hard
port
duck
bugs
bail
mast
thin
lean
fire
read