Why does eye become eyed in 'the blue-eyed boy'? Also, 'the three-legged dog', are there any rules to creating these forms?
NOT A TEACHER
(1) I have
not found a "rule," but I have found
a little information.
(2) You can change some nouns to an adjective by adding the letters
-ed
at the end:
The city has a
wall. It is a wall
ed city.(A special ending such as
-ed,
-ing, etc., is called a SUFFIX.)
(3) You can do this to some noun phrases, too:
Tom has blue eyes. Therefore, he is a blue-ey
ed man.
(4) As you have already guessed, when
-ed is used this way
with a noun or noun phrase,
-ed = "having."
***
This information comes from
A Comprehensive Grammar of the English
Language, by Professor Randolph Quirk et. al. It is
not recommended
for beginning learners.
If you google "English suffixes," you will probably find more information
about the suffix
-ed.