WordNet sense 1 (unable to speak temporarily):

dumb, speechless

WordNet sense 2 (expressed without speech; especially because words would be inappropriate or inadequate):

mute

WordNet sense 3 (unable to express yourself clearly or fluently):

incoherent

WordNet sense 4 (unable to speak because of hereditary deafness):

silent

WordNet sense 5 (without or deprived of the use of speech or words):

unarticulate