Fewer and Hardly a

Fewer adjective - (comparative of `few' used with count nouns) quantifier meaning a smaller number of.

Hardly a and fewer are semantically related. In some cases you can use "Hardly a" instead an adjective "Fewer".

Hardly a adjective - Very few.

Fewer and hardly a are semantically related. You can use "Fewer" instead an adjective phrase "Hardly a".