Speechless, a. — Webster enters it under “speechless”
1. Destitute or deprived of the faculty of speech.
2. Not speaking for a time; dumb; mute; silent. Speechless with wonder, and half dead with fear. Addison. -- Speech"less*ly, adv. -- Speech"less*ness, n.
Shades of meaning
Fernald lists speechlessness only as an antonym, under speech.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given