obmutescence
/ˌɒbmjuːˈtɛsns/noun
The state or condition of becoming mute, speechless, or dumb, especially obstinately or wilfully so.
Origin
Mid 17th century; earliest use found in Thomas Browne (1605–1682), physician and author. From classical Latin obmūtēscere to become dumb or mute + -ence; compare -escence.