19 across
I
must
sit
in
oily
car
(4)
I must sit in oily car (4)
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The definition is at the end of the clue.
How the clue works
Look at car at the end — that's your definition, the Italian motor brand. The wordplay has I (straight from "I must sit in") tucked inside FAT (oily), giving you F-I-AT.