Definition of betaine:
(n) :
(uncountable, organic chemistry) A sweet, crystalline compound (not an alkaloid), trimethylammoniumacetate, found in sugar beet and similar plants, sometimes used to treat muscular degeneracy; the zwitterion (CH₃)₃N⁺CH₂COO⁻
(n) :
(countable, organic chemistry) Any derivative of this compound.
(n) :
(countable, organic chemistry, by extension) Any similar compound, based on sulfur or phosphorus etc, having an onium ion with no hydrogen atom adjacent to the anionic atom.