second nature (n.) Look up second nature at Dictionary.com
late 14c., from Latin secundum naturam "according to nature" (Augustine, Macrobius, etc.), literally "following nature;" from medieval Aristotelian philosophy, contrasted to phenomena that were super naturam ("above nature," such as God's grace), extra naturam ("outside nature"), supra naturam ("beyond nature," such as miracles), contra naturam "against nature," etc.