the.com/totality

means The state or condition of being whole, complete, or absolute — or, in eclipse terms, the brief phase when the moon fully covers the sun's disk.

from Built from Latin totus, 'whole' or 'entire,' which also gave English 'total.' The abstract noun 'totality' emerged in the 1600s to mean 'the whole amount of something.' Its eclipse-specific sense — the exact window of full coverage — is a later, more literal borrowing: astronomers needed a word for the moment the sun's disk becomes totally, not partially, obscured, and the existing word for 'wholeness' was simply waiting there, ready-made.