See my first post then, which seems to have got a little lost in the singular/plural discussion, and how I expect it stems from the "finals" turn - those nice pre-tricycle undercarriage curved approaches, where the final approach was the finals turn, and having nothing to do with the plural of final at all...
That's interesting, but still: why "finals" turn and not "final" turn? I'm more confused now than before... :-?
I will accept that the oval or racetrack pattern and the terminology probably originated at the CFS... I think prior to that almost all airfields were circular or at least arranged so pilots more or less circled in and landed straight into the wind.