at a loss for words

speechless

inarticulate incoherent mum mute quiet silent soundless tongue-tied uncommunicative voiceless wordless

speaking

affected beaten buried conquered defeated overthrown swamped taken

blown-away bowled-over speechless swept off one's feet unable to continue

indifferent unbothered unconcerned unflappable unmoved

amazed astounded dazed dumbfounded garbled mute shocked shy stammering

aghast bashful choked up dumbstruck inarticulate mum silent speechless uncommunicative voiceless