Can you imagine how many times I have been told "but you don’t sound sad."
Students of English are well aware that words are constantly changing their meaning. The adjective sad, for example, had in Old English the meaning of ‘satiated, full to repletion’. A man who has had his fill of pleasure loses his restlessness and excitability. He may become calm and serious, discreet and so trustworthy, the common meaning of the word in Middle English.
Shakespeare uses sad as the opposite of merry and by the seventeenth century the word had become restricted to its modern meaning of ‘mournful’.
As the surname Sadd is found as early as 1086, it must have one of the two earlier meanings.
The Origins of English Surnames