Moving house? (6,4)

I think it could be either:

Which length description are you looking for?:

6,4

caravan

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This might be a double definition.

'moving' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

'house?' is the second definition.
(I know that Caravan is a type of house)

Can you help me to learn more?

(Other definitions for caravan that I've seen before include "House on wheels" , "Trailer with living quarters" , "Towable home" , "Towed accommodation" , "Camel train" .)

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