Definition: "Essential oil"

This is a charade - where two or more separate parts are joined together to form the complete answer.

Look for 'mass of ice' (4 letters) + 'a' + 'car test' (3 letters). The words combine in order to spell out the type of essential oil.

Answer: BERGAMOT | BERG (mass of ice) + A + MOT (car test) = BERGAMOT, which is an essential oil used in perfumes and Earl Grey tea.