Five hundred is a right initial measure to render powerless (6)

I believe the answer is:

disarm

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'render powerless' is the definition.
I can't tell whether this defines the answer.

'five hundred is a right initial measure' is the wordplay.
'five hundred' becomes 'D' (Roman numeral for 500).
'a right' becomes 'ar' (I've seen this in other clues).
'initial' suggests taking the first letters.
The first letter of 'measure' is 'm'.
'd'+'is'+'ar'+'m'='DISARM'

'to' acts as a link.

Can you help me to learn more?

(Other definitions for disarm that I've seen before include "Demilitarise" , "Defuse" , "Take weapons from or captivate" , "Make less hostile, win over" , "Pacify" .)

I've seen this clue in the Sydney Morning Herald.

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