lact-

Lact- 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.

Lact- 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 lact-?

Lact- is a variant of lacto-, which loses its –o– when combined with words or word elements beginning with vowels.

A less common variant of lact-, 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 on lacto- and lacti-.

A term you may have encountered that uses the form lact- is lactose, “a disaccharide present in milk.”

We already know that lact- means “milk,” and the -ose part of the word is used to denote the names of sugars and other carbohydrates. Lactose literally translates to “milk sugar.”

What are some words that use the combining form lact-?

• lactarian
• lactary (using the equivalent form of lact- in Latin)
• lactase
• lactation (using the equivalent form of lact- in Latin)
• lacteous (using the equivalent form of lact- in Latin)
• lactone

What are some other forms that lact- may be commonly confused with?

• galact-
• galacto-

The suffix -eous means “composed of” or “resembling.” With this in mind, what does lacteous mean?