Darling and One and only

Darling noun - A person or thing that is preferred over others.

One and only and darling are semantically related in sweetheart topic. In some cases you can use "One and only" instead a noun "Darling".

One and only adjective - Eminent beyond or above comparison.

Darling and one and only are semantically related in someone adored topic. Sometimes you can use "Darling" instead a noun phrase "One and only", if it concerns topics such as person whom another loves.