Synonyms for Activity (same or very similar meaning)
WordNet sense 1 (the state of being active):
action, activenessWordNet sense 2 (a process existing in or produced by nature (rather than by the intent of human beings)):
natural action, natural processWordNet sense 3 (an organic process that takes place in the body):
bodily process, bodily function, body processFrom the ODE community, based on WordNetadd/edit