Old man’s code word for a pee (4)

I believe the answer is:

papa

I believe this is a double definition.

'old man's' is the first definition.
(synonyms)

'code word for a pee' is the second definition.
(NATO phonetic alphabet codeword for the letter P)

(Other definitions for papa that I've seen before include "Father; P (radio comms.)" , "Pop" , "Father; letter P" , "The old man" , "Mama's other half?" .)

I've seen this clue in The Times.

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