Approximant
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noun.
A speech sound, such as a glide or liquid, produced by narrowing but not blocking the vocal tract, as by placing an articulator, such as the tongue, near another part of the vocal tract.
The Century Dictionary and Cyclopedia
Approaching in character; approximating.
Wiktionary, Creative Commons Attribution/Share-Alike License
noun.
a
consonant
sound
made by slightly narrowing the vocal tract, while still allowing a smooth flow of air.
Liquids
and
glides
are approximants.
noun.
An
approximation
to the solution of a function, series, etc.
Word Usage
"Remember the sonority hierarchy: fricative approximant vowel."
Etymologically Related
consonant
glide
liquid