Cardinal in all sections of Voluntary Service Overseas (4)

I believe the answer is:

five

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'cardinal in' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
I also know that 'cardinal' relates to this answer.

I cannot understand how the remainder of the clue works.

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(Other definitions for five that I've seen before include "Prime number" , "Cube root of 125" , "Cardinal" , "Top-quality hotel has these stars" , "Fourth part of score" .)

I've seen this clue in The Times.

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