• WordNet 3.6
    • v subvocalize articulate without making audible sounds "she was reading to herself and merely subvocalized"
    • ***


In literature:

I let out a subvocal squeal and was pitched forward as the ride system shuddered to a stop.
"Down and Out in the Magic Kingdom" by Cory Doctorow
The SUBVOCALS and ASPIRATES are shown in the vertical columns of the table below.
"Orthography" by Elmer W. Cavins
Malone jerked a little under the doctors calm hands, and swore subvocally.
"Out Like a Light" by Gordon Randall Garrett
Hayden does not distinguish the subvocal and aspirate th in Omaha.
"The Dakotan Languages, and Their Relations to Other Languages" by Andrew Woods Williamson

In news:

Local columnist T.J. Ray proudly touts his Intercranial Kumquat Subvocal 007 Transducer as an option to cellphones ringing in while you're in church, the movies, a restaurant, et cetera.
Talking without moving the mouth is called subvocal speech.