The term 'unable to speak' can be described by three words: MUTE (4 letters), DUMB (4 letters), and TONGUETIED (10 letters). MUTE refers to a person who is unable to produce sound due to a physical disability or medical condition. DUMB is an archaic term used to describe someone who is unable to speak, usually due to a physical disability or medical condition. Tonguetied is a phrase used to describe someone who is unable to speak due to being overwhelmed with emotion or fear.