accidental vs by accident

accidental

adj
  • Happening by chance, or unexpectedly; taking place not according to the usual course of things; by accident, unintentional. 

  • Occurring sometimes, by chance; occasional. 

  • Being a double point with two distinct tangent planes in 4-dimensional projective space. 

  • Adjusted by one or two semitones, in temporary departure from the key signature. 

  • Pertaining to accident and not essence; thus, inessential; incidental; secondary. 

  • Nonessential to something's inherent nature (especially in Aristotelian thought). 

noun
  • Those fortuitous effects produced by luminous rays falling on certain objects so that some parts stand forth in abnormal brightness and other parts are cast into a deep shadow. 

  • A property which is not essential; a nonessential; anything happening accidentally. 

  • A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note. 

  • Part of a text that has a mainly structural purpose, such as spelling, punctuation, or capitalization. 

by accident

adj
  • Accidental; as the result of some unforeseen happening or series of events; unexpected; resulting from an event without the foresight, expectation, aid, or design of the person by whose agency it was caused; unintentional. 

adv
  • As the result of some undesigned, unintended, unrelated, natural, or random occurrence; as the unexpected and unforeseen result of formerly unrelated factors. 

  • By chance; unexpectedly; as the result of an unrelated series of events. 

  • Accidentally; unintentionally; without meaning to; as the result of an event not expected, aided, or willingly planned. 

How often have the words accidental and by accident occurred in a corpus of books? (source: Google Ngram Viewer )