Few and Unfrequent

Few adjective - A quantifier that can be used with count nouns and is often preceded by `a'; a small but indefinite number.

Unfrequent and few are semantically related in hardly any topic. In some cases you can use "Unfrequent" instead an adjective "Few".

Few and unfrequent are semantically related in irregular topic. You can use "Few" instead an adjective "Unfrequent", if it concerns topics such as exceptional, on and off. rare substitute