Longfellow restricts movement. (3)

I believe the answer is:

boa

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'movement' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for boa that I've seen before include "Large reptile" , "... cold-blooded creature" , "S American snake that crushes its prey" , "native American" , "Feathered neckwear - snake" .)

I've seen this clue in The Irish Times.

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