Held up though the road is finished (7)

I believe the answer is:

waylaid

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'held up' is the definition.
Although both the answer and definition are past participle verbs, I don't understand how one could define the other.

'the road is finished' is the wordplay.
'the road' becomes 'way' (I've seen this in other clues).
'is finished' becomes 'laid' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'way'+'laid'='WAYLAID'

'though' acts as a link.

Can you help me to learn more?

(Other definitions for waylaid that I've seen before include "Aggressively intercepted" , "Ambushed" .)

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

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