inadvertently
Inadvertently (adverb) means By accident; without meaning to; as a result of not paying attention. Example: “She inadvertently left her phone on the train.”
How to use inadvertently
Learner’s notesIn plain EnglishDoing something by accident or oversight, not on purpose.
Don't confuse with "inadvertently" meaning careless on purpose — it always implies the act was unintentional.
Fill the gap
Can you complete this real example?
She _____ left her phone on the train.
Etymology
From inadvertent plus the adverb-forming suffix -ly.