There is a difference. I own one of each.
Monolever are single swing arm airheads from the late 80 all the way through 95. They came in R, RT and RS configuration. With the introduction of the 92 R100R and GS came the Paralever rear end, which were fore runners to the 1100 series. The only Paralever design bikes in airheads are the R and GS, the RT remained a monolever. The best way to see the difference is in color and external size. Monolever's were black, Paralever's were silver. Monolever's are much skinnier when compared to a paralever. There are also mechanical differences between the two. Monolevers have oil, paralevers are dry; in addition you can mate different rear ends to the monolever, but that is not available for paralevers.
Hope that makes sense.
1986 R 80RS (monolever)
1992 R 100 R UK model (paralever)