.

Keeping this in view, did not reply or didn't replied?

In your example, on the other hand, the two expressionsgive two (slightly) different impressions: "he has notreplied yet" means "I still hope that he would reply,because (for example) he is a little busy but willeventually reply, as he always do" while, on theother hand, "he has not yet replied" meanssomething

Beside above, how do you use not yet in a sentence? Put “yet” at the end of asentence to describe something that hasn't happened. It isoften used in negative statements in which you use anegative term like “have not” or “hasnot.” For example, you may say, “I haven'tcompleted my homework yet” or “I haven't eatenbreakfast yet.”

Then, which is correct response or respond?

Response is the noun while respond is theverb. So, when you respond to something, you are giving aresponse. Response is the noun. It may mean thereaction to something or an answer given to aquestion.

What does have not yet mean?

"Have not yet to" is grammatically incorrect."Have not yet" is correct, which means that there is someactivity, task or event, which has not started yet.For example: I have not yet begun to do my homework.This sentence means that you want to do your homework buthave not started doing it yet.