Ultraviolet and Unperceivable

Ultraviolet adjective - Having or employing wavelengths shorter than light but longer than X-rays; lying outside the visible spectrum at its violet end.

Unperceivable and ultraviolet are semantically related. In some cases you can use "Unperceivable" instead an adjective "Ultraviolet".

Unperceivable adjective - Impossible or difficult to perceive by the mind or senses.

Ultraviolet and unperceivable are semantically related. You can use "Ultraviolet" instead an adjective "Unperceivable".