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border (up)on something
1. Lit. [for something] to touch upon a boundary. (Upon is more formal and less commonly used than on.) Our property borders on the lakeshore. The farm borders upon the railroad tracks.
2. Fig. [for some activity or idea] to be very similar to something else. (Not usually physical objects. Upon is formal and less commonly used than on.) This notion of yours borders upon mutiny! That plan borders on insanity.
border on something
to be similar in quality or character I thought the author's criticism bordered on rudeness.
Usage notes: usually used about negative qualities
border onor border upon
1. To be next to something in location: New York State borders on Lake Ontario. My property borders upon a small lake.
2. To come close to being something, especially in association, meaning, or intent; verge on something: Your harsh criticism borders on being offensive. Some of their jokes were funny, but others bordered upon the ridiculous!