What is 40th?
Noun - A Unit of Time = 1 hour in a 40 hour work week (ie. 1/40)
You begin work at 8am on a Monday morning. At 9am a co-worker looks ("prairie-dogs") over the cubicle wall and suggests getting a cup of coffee. The co-worker then states "How's it going?" and you reply "Great. Only 39/40ths until the week is over."