1. முடியவில்லை (mudiyavillai): This is the most common and general translation of "could not". It expresses the inability to do something.
2. சாத்தியமில்லை (saathiyamillai): This means "it is not possible", implying that something is impossible to achieve.
3. கூடாது (koodaathu): This means "must not" or "should not", implying that something is forbidden or not allowed.
4. என்றும் இல்லை (enrum illai): This means "never" and implies that something was never possible or never happened.
5. சாத்தியமில்லா (saathiyamilla): This is the adjective form of "சாத்தியமில்லை" and means "impossible".
Examples:
* நான் அதைச் செய்ய முடியவில்லை (naan adhaicha seyyamudiyavillai): I could not do that.
* அது சாத்தியமில்லை (athu saathiyamillai): It is not possible.
* நீ அங்கு போகக்கூடாது (nee angu pogakkoodaathu): You should not go there.
* அவன் அதை என்றும் இல்லை (avan adhai enrum illai): He never did that.
* அது சாத்தியமில்லா (athu saathiyamilla): It is impossible.
The specific meaning of "could not" will depend on the context and the specific word used in the sentence.