semivowel

/S EH0 M AY0 V AW1 AH0 L/
noun
  1. 1

    A sound in speech which has some qualities of a consonant and some qualities of a vowel.

  2. 2

    A letter which represents a semivowel sound, such as w or y in English.

Source: https://en.wiktionary.org/wiki/semivowel