an act of killing oneself; suicide ...1692 obs.
from self- + -cide (forming nouns with the sense ‘the killing of the person, animal, etc.)’, as an alteration of suicide
FIRST DOCUMENTED USE
1692 - see EXAMPLE below
"...The author several times saith that the law of nature is the law of God, and yet all wickedness is lawful by the law of nature. - That no Homicide, or Selfcide, or Fratricide, or Patricide is against the law of nature. If so, 'tis a wise law thar forbids nothing. Also that there must be a law of God winking at most unnatural impieties..."
From: Athenae Oxonienses. An Exact History of All the Writers and Bishops, Who have had their Education in The most ancient and famous University of Oxford, From the Fifteenth Year of King Henry the Seventh, Dom. 1500, to the End of the Year 1690
By Anthony Wood