A rare term possibly referring to the act of bringing into agreement or making things accord with each other.
Potentially from 'agre' (agreement) + -ation (noun suffix indicating action or process). This appears to be an extremely rare or obsolete formation in English lexicography.
This word might be a ghost word—a term recorded in historical dictionaries that never actually had widespread use or whose historical presence is questionable. Lexicographers occasionally find such fossils when researching word origins.
Complete word intelligence in one call. Free tier — 50 lookups/day.