Dearest and One and only

Dearest noun - A beloved person; used as terms of endearment.

One and only and dearest are semantically related In some cases you can use "One and only" instead a noun "Dearest".

One and only adjective - Eminent beyond or above comparison.

Dearest and one and only are semantically related in sweetheart topic. Sometimes you can use "Dearest" instead a noun phrase "One and only", if it concerns topics such as darling, someone adored.