inadvertent - adjective
Example: Though his mistake was inadvertent, it was also costly.
"inadvertent - correct spelling." Grammar.com. STANDS4 LLC, 2017. Web. 24 Nov. 2017. <http://www.grammar.com/inadvertent-correct-spelling>.
It’s now more important than ever to develop a powerful writing style. After all, most communication takes place in reports, emails, and instant messages.