canon

From Middle English canoun, borrowed from Old French canon and Old English canon, both from Latin canōn, from Ancient Greek kanṓn meaning 'measuring rod, standard,' related to kánna, 'reed,' and ultimately tracing to a Semitic root for reed, as in Hebrew qane and Arabic qanāh.

A word for a straight, measurable reed became the word for the standard or rule used to judge things, and later the accepted body of texts or works taken as authoritative.

It's a doublet of qanun, and shares roots with cane, cannon, canyon, and canal, all descending from that same reed-and-measuring-rod family.