lacto-

American  

1. a combining form meaning “milk,” used in the formation of compound words (lactometer ); specialized in chemical terminology to mean “lactate,” or “lactic acid.”

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lacto- British  

combining form

1. indicating milk

   lactobacillus

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Usage

What does lacto- mean? Lacto- is a combining form used like a prefix meaning “milk.” In terms from chemistry, it used to specifically mean "lactate" or "lactic acid." It is often used in scientific and medical terms. Lacto- comes from Latin lac (stem lact-), meaning “milk.” The Latin cognate of lac is gála (stem galakt-), also meaning “milk,” which is the source of galaxy. To learn more, check out our Words That Use articles on galacto- and galact-. What are variants of lacto-?When combined with words or word elements that begin with a vowel, lacto- becomes lact-, as in lactose. A less common variant of lacto-, when combined with some words or word elements that begin with a consonant, is lacti-, as in lactifuge. Want to know more? Read our Words That Use articles about lact- and lacti-.

Etymology

Origin of lacto-

< Latin lact- (stem of lac milk) + -o-