Intimacy derives from the Latin intimus ("within", "inside", "innermost", "deepest"" combined with the suffix -cy.  It signifies a state of close, personal, or familiar connection, originating from the root intus ("within"). The term evolved from the concept of being "inmost" or having deep, internal knowledge.  It is rooted in the Late Late Latin verb intimare ("to make known", "announce", "Impress", "bring into").  The adjective "intimate" appeared in the 1630s meaning "closely acquainted", while the noun "Intimacy" arrived in the 1640s.   While the origianal meaning of intimacy indicated a close, personal friendship (1640s), the specific context of sexual intercourse appeared later, by the 1670s, becoming common by the late 19th century.  Intimacy generally refers to a deep, close relationship involving shared personal, private, or familiar feelings. 

According to the Oxford English Dictionary (OED), the noun intimacy was first used in English in the mid-1600s, with the earliest evidence dating back to 1641 in the writing of John Jackson. The term is derived from the adjective intimate, which appeared earlier in the 17th century.   According to the Oxford English Dictionary (OED), the earliest known use of the verb intimate is in the mid-1500s. 

The importance of incorporating intimacy—defined as deep emotional, physical, mental, or spiritual closeness—early in a story serves to immediately forge a bond between characters and readers, setting the stakes for the narrative. Rather than just sexual encounters, early intimacy includes vulnerability, shared secrets, or profound conversations that reveal character motivations and establish the "why" behind their actions. 

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INTIMACY Definition & Meaning - Merriam-Webster

INTIMACY Synonyms: 37 Similar and Opposite Words | Merriam-Webster Thesaurus

INTIMATE Definition & Meaning - Merriam-Webster