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Webster 1913 Edition
Proto-
Pro′to-
.1.
A combining form prefix signifying first, primary, primordial;
as,
proto
martyr, the first martyr; proto
morphic, primitive in form; proto
plast, a primordial organism; proto
type, proto
zoan.2.
(Chem.)
(a)
Denoting the first or lowest of a series, or the one having the smallest amount of the element to the name of which it is prefixed; as protoxide, protochloride, etc.
(b)
Sometimes used as equivalent to mono-, as indicating that the compound has but one atom of the element to the name of which it is prefixed. Also used adjectively.