happen (v.) Look up happen at Dictionary.com
late 14c., happenen, "to come to pass, occur, come about, be the case," literally "occur by hap, have the (good or bad) fortune (to do, be, etc.);" extension (with verb-formative -n) of the more common hap (v.). Old English used gelimpan, gesceon, and Middle English also had befall. In Middle English fel it hap meant "it happened." Related: Happened; happening. Phrase happens to be as an assertive way to say "is" is from 1707.