Slowly pay off armies to disband (8)

I believe the answer is:

amortise

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'slowly pay off' is the definition.
I can't tell whether this definition defines the answer.

'armies to disband' is the wordplay.
'disband' indicates anagramming the letters (I've seen 'disbanded' mean this (I've seen this in other clues)).
'armies'+'to'='armiesto'
'armiesto' with letters rearranged gives 'AMORTISE'.

Can you help me to learn more?

(Other definitions for amortise that I've seen before include "Gradually write off initial costs" , "Liquidate gradually" .)

I've seen this clue in The Guardian.

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