in accordance with what is appropriate or suitable for the circumstances
"he was appropriately dressed"
"If you don't behave properly, you'll have to leave!"
"I met the junior senator from Illinois and I was duly impressed"
In a due, fit, or becoming manner; as it ought to be; properly.
"The ambassador received his host with duly respectful attention."
In plain English: Duly means doing something exactly when it is supposed to happen and following all the right rules.
"He duly signed the contract before leaving the office."
Usage: Use "duly" to emphasize that an action was performed at the correct time and in the proper way according to established rules or expectations. It often appears after verbs like pay, sign, or receive to confirm compliance with a procedure.
Duly comes from the Middle English word duely, which meant "rightly" or "properly." It traveled into modern usage by combining the adjective due with the suffix -ly.