Legal order from fellow to block American (8)

I believe the answer is:

mandamus

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'legal order' is the definition.
The definition suggests a singular noun which matches the answer.

'fellow to block american' is the wordplay.
'fellow' becomes 'man' (I've seen this before).
'to block' becomes 'dam' (damming is a kind of blocking).
'american' becomes 'us' (**).
'man'+'dam'+'us'='MANDAMUS'

'from' is the link.

Can you help me to learn more?

(Other definitions for mandamus that I've seen before include "Legal requirement" , "writ" .)

I've seen this clue in The Telegraph.

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