At one time and One

At one time adverb - At a previous time.

One and at one time are semantically related. in in the past topic. In some cases you can use "One" instead an adverb phrase "At one time".

One adjective - Being the one or ones of a class with no other members.

At one time and one are semantically related. Sometimes you can use "At one time" instead an adverb "One".