What is possessing some quality, or having been subject to some operation (as substitution), in the second degree; as, a secondary salt, a secondary amine, etc. Cf. primary called?

secondary — (Chem.) Possessing some quality, or having been subject to some operation (as substitution), in the second degree; as, a secondary salt, a secondary amine, etc. Cf. primary. (Webster's 1913.)

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