Enter a clue or pattern or both:
The Clue
By accident (10 letter answer)
The Answer
MISTAKENLY
Tags
Notes
The answer MISTAKENLY is so rare that it appears less than once every 2500 puzzles.
Definition
MISTAKENLY as an adverb:
1. (mistakenly, erroneously) = in a mistaken manner; "he mistakenly believed it"