to a complete degree or to the full or entire extent (`whole' is often used informally for `wholly')
"he was wholly convinced"
"entirely satisfied with the meal"
"it was completely different from what we expected"
"was completely at fault"
"a totally new situation"
"the directions were all wrong"
"it was not altogether her fault"
"an altogether new approach"
"a whole new idea"
"she felt right at home"
"he fell right into the trap"
so as to be complete; with everything necessary
"he had filled out the form completely"
"the apartment was completely furnished"
In a complete manner
"She completely finished the puzzle before her friends even arrived."
In plain English: Completely means doing something all the way through with nothing left over.
"I completely forgot to lock the door before leaving."
Usage: Use completely to describe an action or state that has happened in its entirety without any part remaining. It functions as an intensifier before adjectives and verbs to indicate total certainty or finish, such as saying the room was completely empty or the task was completely finished.
The word completely is formed by adding the suffix -ly to the adjective complete. It entered English as a straightforward combination of these two existing parts to create an adverb meaning entirely or totally.