1. a basic fact or assumption that you accept as being true
you can/can't take that as a given
Something which is 'a given' is known to be true. When you have already accepted that something is true, or if you have come to a conclusion and you want to move on from it, you can say that the matter at hand is 'a given'. This just means that it is not up for dispute or open for argument. Climate change scientists would say that the fact that the ice caps are melting faster is 'a given'. They accept it to be true. You will hear this used in many contexts, social or professional.