intromission

Short definition from Wiktionary

Noun

1. 1
   The state of being allowed to enter; admittance
2. 2
   The act of allowing to enter; admission
3. 3
   Putting one thing into another; introduction (into); insertion
4. 4
   Copulation: usually the first moment of initial entry of a penis into a vagina, mouth or anus.
5. 5
   An intermeddling with the affairs of another, either on legal grounds or without authority.