Speechless means so struck by a feeling that no words come out. The feeling is usually strong: shock, anger, joy, disgust, or being deeply moved. It is a moment, not a condition — you are speechless for a second or two, then you find your words again. English uses it much more for the emotion than for the silence itself; when someone says 'I was speechless', they are really telling you how strongly they felt, and the silence is the evidence. It works for good and bad feelings both. 'The view left me speechless' is delight. 'I was speechless when he asked me to pay for his lunch' is outrage. Without any other clue, though, listeners usually lean towards the bad-feeling reading. There is a second, literal meaning that is rarer and more medical or poetic: unable to speak at all, having no power of speech. The old Old English word covered this sense plainly. Today a doctor would say 'unable to speak' or 'nonverbal', and 'speechless' has drifted almost entirely to the emotional use. You will meet it in fixed patterns: leave someone speechless, be speechless with rage/anger/shock, be rendered speechless (formal), and simply 'I'm speechless' as a whole reply on its own.