The word "onerosity" is a relatively uncommon term that refers to the state of being burdensome or oppressive. While synonyms for this specific word are limited, there are alternatives that capture similar meanings. "Burdensomeness" denotes the quality of being burdensome or causing difficulty, while "oppressiveness" suggests a heavy or overwhelming nature. Additionally, the words "weightiness" and "heaviness" can be used to convey the concept of being oppressive or onerous. While it may be challenging to find numerous synonyms for "onerosity", these alternatives effectively communicate the sense of being burdensome or difficult.