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The pronunciation of any word in English (or any language at all) is not Universal.  This is because there are many different dialects of The English Language — both throughout America, and also world-wide.  The pronunciations that are presented on GiveMeSomeEnglish!!! are based-upon a combination of both “common usage”, and the most neutral accent used in The International Common Tongue — a.k.a. “American English”.
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Accidental – For this word:  the “A” is short;  for the “cc” combination — the first “c” is hard, and the second “c” is soft (this is one of TWO standard pronunciations of this letter combination in The Common Tongue);  then, the “i” turns into an i-schwa;  the “e” is short;  and for the “-al” suffix – the “a” turns into a true-schwa (this is the standard pronunciation of this suffix in The Common Tongue).

– /æK-sih-dehn-təl/ – /ˈæk.sə(ɪ).ˈdɛn.təl/ – Notice also that the stress is on the third syllable –

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See Also:  Accident, & Accidental

Learn More About The Word “Accidentally” On Wiktionary

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