What is "devocalize"

Devocalize \De*vo"cal*ize\, v. t. To make toneless; to deprive of vowel quality. -- De*vo`cal*i*za"tion, n.

If we take a high vowel, such as (i) [= nearly i of bit], and devocalize it, we obtain a hiss which is quite distinct enough to stand for a weak (jh).
--H. Sweet.

vb. 1 (context transitive English) To make toneless; to deprive of vowel quality. 2 (context transitive English) To reduce the volume of the vocalizations of (an animal) by surgically removing tissue from its vocal cords.