The hint says oğul, but the correction says oğlu
The word for "son" is oğul. "oğlu" has the 3rd person possessive suffix on it.
The hints are not personalized for every sentence :)
Is oğul irregular? I would expect to see oğulu.
Yep, there are a lot of two syllable words that drop the second vowel when you add a suffix that begins with a vowel. Other example are: şehir (city), omuz (shoulder), and ağız (mouth)
Can it also be oğludur?
why is there not a possessive ending to oglu
There is. "Son" is oğul -- but it loses a vowel when you attach the possessive ending.
I listed a few similar cases at https://forum.duolingo.com/comment/11938813.
Shouldn't it be oğlusu?
"Son" is oğul -- so you do not need the buffer-s at all. But then vowel loss impacts the first "u."
Why ''Kuzem teyzemin oğludur'' is wrong?
kuzen = cousin
kuzenim = my cousin
Kuzenim and benim kuzenim are the same thing why's wrong?
Both are accepted in otherwise correct sentences. Was there another error in your answer?
Has the character â mostly fallen out of use? We sometimes see it in lâle (tulip) and hâlâ (father's sister), right?
I used halamin and it was not accepted, why
You must have entered something other than "Kuzenim, halamın oğlu," because this was just accepted for me.