This Greek adjective describes what is natural or inborn, in contrast to what is taught, learned, or conventional. In Romans 1:26-27, Paul uses it to describe the 'natural use' of human sexuality, contrasting it with what is 'contrary to nature.' The word carries philosophical weight from classical Greek, where it distinguished between what exists by nature (physis) versus by convention (nomos). In 2 Peter 2:12, it describes creatures that are 'natural' or 'instinctive' in their behavior, acting according to their created nature rather than rational thought.