by chance

Adverb

• without advance planning
  • they met accidentally
    

• by accident
  • betrayed by a word haply overheard
    

• through chance, "To sleep, perchance to dream.."

Related words

• Synonyms: 
  accidentally , circumstantially , unexpectedly , haply , by luck , perchance
• Antonyms: 
  intentionally , deliberately , designedly , on purpose , purposely , advisedly , by choice , by design