Contemporaneousnesses essentially means existing or occurring at the same time. The antonyms for contemporaneousnesses would, therefore, refer to occurrences that are not simultaneous. Antonyms for this word could include terms such as outdated or obsolete, referring to things that no longer exist in the present or are no longer considered relevant. Conversely, words such as futuristic or avant-garde could describe things that have not yet occurred but are expected to happen in the future. Words such as sequential or staggered could also be used as antonyms for contemporaneousnesses, indicating events that occur in a particular order or time frame, rather than simultaneously.