[noun] (chemistry) the capacity of a substance to take part in a chemical reaction; "catalytic activity"
[noun] a process existing in or produced by nature (rather than by the intent of human beings); "the action of natural forces"; "volcanic activity" Synonyms:natural process, natural action, action
[noun] the trait of being active; moving or acting rapidly and energetically; "the level of activity declines with age" Synonyms:activeness