"Security" originates from the Latin securus, meaning freedom from anxiety ( se ("without" or "free from") + cura ("care", "worry", or "anxiety").  Emerging in English during the early 15th century.  Originally, it implied being "free from care" or "unconcerned," which often meant being "over-confident" or careless, rather than just physical safety.  Over time the meaning evolved as follows: 15th century: Referred to a state of being safe or free from anxiety.  16th/17th Century: Used as "surety" or "guarantee" of a promise.  Modern Usage: Shifted towards physical protection, defense, and financial instruments.  The concept of security was originally a mental state—a feeling of being untroubled—before it became a term describing physical protection or financial stability.   "Surety" and "Secure" are closely related, sharing the same Latin origin through different paths. 

According to the Oxford English Dictionary (OED), the earliest known use of the noun security is in the Middle English period (1150-1500), with the earliest evidence dating from before 1425.  The word appears in Dialogue Reason & Adversity.  The related term "non-security" also dates from the Middle English period, specifically before 1420.  "Security" vs "Safety": While security appeared in the early 15th century, the noun safety also stems from the Middle English period, with evidence for it found around 1380. 

Character security—referring to a character's emotional, psychological, or physical "shielding" (such as secrets, fears, or defense mechanisms)—is crucial for creating engaging, relatable, and believable stories.  It acts as the foundation for a character’s motivations and reactions, driving the narrative forward through internal and external conflict.