Surely this has been asked before, but my searches did not find the right threads.

My question is whether I can use the return portion of a R/T ticket if I did not use the outbound portion? Last minute change in plans caused me to take a one-way flight on different carrier to my destination and now I still have the entire ticket from the original plan and would like to use the return portion only. A one-way return home is far too expensive.

Any help is definitely appreciated.