29 across
Essential
oil
for
a
car
test
on
mass
of
ice
(8)
Essential oil for a car test on mass of ice (8)
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The definition is at the beginning of the clue.
How the clue works
Look at Essential oil — that's your definition, pointing to a citrus oil. For the wordplay, you've got BERG (mass of ice) followed by A and then MOT (car test), stringing them together to give you BERG + A + MOT.