Bound, aged gentleman's manacled (4)

I believe the answer is:

edge

I'm a little stuck... Click here to teach me more about this clue!

'bound' is the definition.
(I know that edge is a type of demarcation)

'aged gentleman's manacled' is the wordplay.
'EDGE' is hidden within the letters.
But, I'm uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for edge that I've seen before include "Keenness" , "Move furtively; intense quality" , "on which one is ill at ease?" , "Intense/striking quality" , "small advantage" .)

I've seen this clue in The Telegraph.

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