For the grammar terms it means the Particular discription.
I will make an exception in this circumstance, with certain reservations.
That's a completely different circumstance.
"They happened to be partnered together by circumstance."
Make sure to note the circumstance I have just said!
"under any circumstance" is the prepositional phrase.
in this situation
Although she never realized it, their first meeting was not by circumstance, but by design on his part.
(The term is more often used as a plural.)The lack of governmental response in the crisis was a rare circumstance of non-intervention.
Mitigating factor.
Under certain circumstance the US government has the right to commandeer private property.
The ancient cultures teacher has absolute power over the class in every circumstance possible.
His arrival was a happy circumstance. He always adapted easily to new circumstances.