Happen ___ (discover)

• "Once" follower, in stories
• Story starter, after ''Once''
• Second word of many a fairy tale
• Word with reflection or my word
• Second fairy tale word
• 'Oncea time ...'
• Well versed in
• "___ a slitted sheet I sit" (tongue twister phrase)

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Upon \Up*on"\, prep.[AS. uppan, uppon; upp up + on, an, on. See Up , and On .] On; -- used in all the senses of that word, with which it is interchangeable. ``Upon an hill of flowers.'' --Chaucer. Our host upon his stirrups stood anon. --Chaucer. ...

Wikipedia Word definitions in Wikipedia