'astrometrical' originates from Modern English formation based on the noun 'astrometry', ultimately from Greek elements 'astron' (star) and 'metron' (measure).

'astrometrical' derives from Medieval/Modern Latin and Greek roots: Greek 'astrometria' ('astron' + 'metron'), -> Late Latin/Modern Latin 'astrometria' -> English 'astrometry' -> adjectival form 'astrometrical'.

Initially it referred specifically to the measurement of stars ('measuring the stars'); over time it has remained focused on the measurement of celestial positions and motions and is used adjectivally to describe related data, methods, or instruments.