One vehicle described as terrible (4)

I believe the answer is:

ivan

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'described as terrible' is the definition.
I can't tell whether this defines the answer.

'one vehicle' is the wordplay.
'one' becomes 'I' (Roman numeral).
'vehicle' becomes 'van' (van is a kind of vehicle).
'i'+'van'='IVAN'

Can you help me to learn more?

(Other definitions for ivan that I've seen before include "Russian, say" , "'Terrible' emperor of Russia" , "A Terrible old Russian ruler" , "... the Terrible, 16th-century ruler of Russia" , "- - the Terrible (Czar)" .)

I've seen this clue in The Globe and Mail.

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