Mrs. – Stands for Mistress, the opposite of Master, which is what a married woman would be called. In some American language traditions, the R is pronounced: Mizrez.
lb. – Pound. Comes from ancient Roman era in Britain: Libra Pondo: A pound by weight.
oz. – Ounce. Originated with the Roman Latin word uncia. In Italian the word became onza and shortened to Oz.
stat – Immediately. Heard on medical TV shows. It comes from the Latin word statium.