The 1955 Urantia Foundation printing had "co-relater" here. The spelling was changed in the second (1967) and following printings. It is possible that the original spelling was a coined extension of "co- relation" and "co-relative," both of which exist.
P1156:5, 105:3.8
7. The Universal Absolute. Unifier of the deified and the undeified;
co-relator of the absolute and the relative.
The Universal Absolute (being static, potential, and associative) compensates
the tension between the ever-existent and the uncompleted.