The sanas of SCAM is "aineoil" and is said to be a "carnival term" which does not enter American English language until 1963

The etymology of SQUARE in figurative sense of "fair play" as in a "square" deal or a "square" [gambling] game allegedly dates back to 1591 in English. Though Barnhart, as usual, provides no citations.

How did the fair and square twin gain admittance to the discourse and the other focal daibhir get the old "eiteachas aíochta?

'S cam (é).
'S cóir (é).

Cúpla ceangailte? Nó camóg? Ceann éigin den dá cheann.