: in an accidental or unintended manner : by accident
I accidentally deleted the file.
The lock prevents the gate from opening accidentally.
Six lionfish were accidentally released from a home aquarium in Biscayne Bay, Fla., during Hurricane Andrew in 1992. Alcestis Cooky Oberg
The Olympic test was thrown out after the test lab accidentally destroyed the backup sample … that's required to confirm a positive result. Christie Aschwanden
He bumped into her accidentally on purpose. [=he bumped into her intentionally but he tried to make it appear to be an accident]