Half-witted and Subnormal

Half-witted adjective - Not having or showing an ability to absorb ideas readily.

Subnormal and half-witted are semantically related In some cases you can use "Subnormal" instead an adjective phrase "Half-witted".

Subnormal adjective - Of a size that is less than average.

Half-witted and subnormal are semantically related in limited topic. Sometimes you can use "Half-witted" instead an adjective "Subnormal".