intromission

English

From (deprecated template usage) [etyl] Latin intro-', "into", + mission, "sending", from Latin missio, from perfect passive participle missus, "sent", from verb mittere, "send", + noun of action -io. Commonly used to refer to the instant at which sexual intercourse begins, when the penis first slides into (enters) the vagina.

intromission (countable and uncountable, plural intromissions)

the state of being allowed to enter; admittance
the act of allowing to enter; admission
putting one thing into another; insertion
- 1888, Henry James, The Reverberator.
  "Your father has told me all about it. Did you ever hear of anything so ridiculous?"
  "All about what?—all about what?" said Delia, whose attempt to represent happy ignorance seemed likely to be spoiled by an intromission of ferocity. She might succeed in appearing ignorant, but she could scarcely succeed in appearing happy.
copulation: normally refers to the first moment of initial entry of a penis into a vagina, mouth or anus.
(law, Scotland) An intermeddling with the affairs of another, either on legal grounds or without authority.

the state of being allowed to enter

putting one thing into another

copulation