The Oxford Thesaurus An A-Z Dictionary of Synonyms - speechlessadj.

1) mute, dumb, voiceless: He was speechless and in shock for two days following the accident. They claim to speak for animals who are, of course, speechless themselves. 2) dumbfounded or dumfounded, dumbstruck or dumbstricken, wordless, struck dumb, tongue-tied, thunderstruck, shocked, dazed, inarticulate, paralysed, nonplussed, Slang Brit gobsmacked: He was speechless with fury to find his car missing.