stem of an adjective; adjectival stem
Linguistics term referring to the base part of an adjective that remains after removing inflectional endings.
The adjectival stem of the Japanese adjective 'takai' is 'taka'.
語幹 is the general term for 'word stem' in linguistics, while 形容詞幹 specifically refers to the stem of an adjective.
Compound of 形容詞 (adjective) and 幹 (stem, trunk). The exact historical derivation is uncertain, but the term is a modern linguistic coinage.