E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Oz. (for ounce).
z made with a tail (3) resembles the old terminal mark 3, indicating a contraction—as vi3. a contraction of vi[delicet]; quib3, a contraction of quibus; s3, a contraction of sed (but), and so on.
