Pee

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late 18th century: euphemistic use of the initial letter of piss.

wiktionary

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The initial letter of piss. Compare eff.

pee (plural pees)

Spelling of the abbreviation p of pence.

See peak.

pee (plural pees)

etymonline

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pee (v.)

1788, "to spray with urine" (trans.), euphemistic abbreviation of piss. Meaning "to urinate" is from 1879. Related: Peed; peeing. Noun meaning "act of urination" is attested by 1902; as "urine" by 1961. Reduplicated form pee-pee is attested by 1923.