noun
semivowel
Linguistics term for a speech sound that is phonetically similar to a vowel but functions as a consonant, such as the 'y' in 'yes' or the 'w' in 'we'.
日本語の「や」の最初の音は半母音です。
The first sound of Japanese 'ya' is a semivowel.
子音 means 'consonant', a sound with obstruction in the vocal tract. 半母音 is a type of consonant that is very close to a vowel.
Compound of 半 (half) and 母音 (vowel), literally 'half-vowel'. The term is a direct translation of the English 'semivowel'.