Spot cash/spot on etc

Spot cash meaning ready money dates from the late 19th century. Spot on meaning completely or accurately dates from the 1920s although Eric Partridge maintains it was originally military terminology from WWII slang meaning right on target. Some sources maintain the expression is much older, from the early 19th century, and derives from ‘spotting’ or placing billiard balls in their correct spots or positions. Spot check is first attested from the 1930s. To put someone on the spot, in a difficult or awkward situation, is American and dates from the 1920s. ‘To spot someone money’ is to loan money and is American slang from the 1930s.