This is the verse translation, not a definition of the individual word.
They ask you [O Prophet] about the Hour, “When will it come to pass?” Say, “Its knowledge is only with my Lord. None can reveal its due time except Him. It will be heavy on the heavens and earth; it will only come to you by surprise.” They ask you as if you are well-aware of it. Say, “Its knowledge is only with Allah, but most people do not know.”