If it has to do with money, it's pecuniary — not to be confused with "peculiarity" — which actually has one more syllable than pecuniary but isn't worth as much because it rarely pertains to money.
Pecuniary seems like a peculiar word for talking about money, but it all adds up when you learn that it was the worth of the cattle, or pecū in Latin, that give pecuniary its meaning. In Roman times livestock served as money in making transactions. Some cultures still have economies based on cattle, but most modern societies have a pecuniary, or money, system based on, well, money.
