peremptorily; forcibly; without giving a choice
Used when someone is forced to do something without being allowed to object or refuse. Often implies a high-handed or coercive manner. Similar to 有無を言わせず, but 有無を言わさず is a slightly more colloquial or emphatic variant.
See also: 有無を言わせず
The boss ordered overtime without giving anyone a chance to object.
He grabbed my arm and dragged me away without letting me say a word.
From 有無 (yes or no, objection) + を + 言わさず (causative-negative of 言う, 'not let say'). Literally 'without letting one say yes or no'.