Where does “P U” come from?

P U (English) comes from French puer, from Old French puir, from Vulgar Latin putire, from Latin pūteō, from Proto-Italic pūtos, from Proto-Indo-European puHtós, from Proto-Indo-European pewH- — to be clean, pure.

P U (English): "What is that awful smell? P U!"

Definitions

"What is that awful smell? P U!"

Ancestry of “P U”, step by step

P U traces back through two separate lines of ancestry.

via French puer

Step	Language	Word	Meaning
1	French	puer	to stink, to smell
2	Old French	puir	to smell (bad); to stink
3	Vulgar Latin	putire	present active infinitive of *putiō
4	Latin	pūteō	to stink, be rotten, putrid
5	Proto-Italic	pūtos	—
6	Proto-Indo-European	puHtós	pure, clean
7	Proto-Indo-European	pewH-	to be clean, pure

via Spanish fu

Step	Language	Word	Meaning
1	Spanish	fu	An indication of disgust; The hissing of a cat

Every word from Proto-Indo-European pewH- →Every word from Proto-Indo-European puHtós →Every word from Proto-Italic pūtos →