say it: ak-TIV-uh-tee
activity is a noun meaning "any specific behavior". It carries 6 recorded senses.
any specific behavior
“they avoided all recreational activity”
an organic process that takes place in the body
“respiratory activity”
(chemistry) the capacity of a substance to take part in a chemical reaction
“catalytic activity”
chemistry
a process existing in or produced by nature (rather than by the intent of human beings)
“the action of natural forces”
“volcanic activity”
the trait of being active; moving or acting rapidly and energetically
“the level of activity declines with age”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for activity come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.