Dumb, mute, speechless, inarticulate mean lacking the power to speak.
Dumb and mute are often used interchangeably, but when used in distinction from each other, dumb implies an incapacity for speech (as in the case of animals and inanimate objects or of human beings whose organs of speech are defective); mute implies an inability to speak, owing to one’s never having heard speech sounds (as in the case of one who is deaf congenitally or has lost his hearing before being old enough to reproduce heard sounds); thus, persons once called deaf and dumb are usually deaf-mutes who have healthy speech organs and can be trained to speak through the senses of sight and touch.
When used of persons who are normally able to speak, dumb (see also STUPID) usually suggests deprivation of the power to speak; mute stresses a compelling cause for keeping or maintaining silence.
Speechless commonly implies momentary deprivation of the power of speech.
Inarticulate implies either lack of the power to speak at all or, especially, inability to speak intelligibly or clearly, usually on account of some powerful emotion but sometimes because of lack of power to express one’s thoughts or feelings.