The building blocks of English

Affixes

lact(o)-

Also lacti‑.

Milk; lactic acid or lactose.

Latin lac, lact‑, milk.

Lactation refers to the secretion of milk by the mammary glands; something lactiferous forms or conveys milk or milky fluids; a hormone or other substance that is lactogenic induces the secretion of milk; a person who is a lacto-ovo-vegetarian (Latin ovum, egg) eats vegetables, eggs, and dairy products but does not eat meat.

A sugar characteristically present in milk is lactose or milk sugar. Fermentation of it by a lactobacillus produces lactic acid. Lactoprotein is the general name for the protein component of milk, constituents of which include lactoferrin, lactoglobulin, and lactalbumin.