An archaic or variant spelling of 'aggregation,' meaning a collection or gathering of separate things into one group.
From Latin 'aggregare' (to add to a flock) from 'ad' (to) + 'gregare' (to gather, from 'gregis' meaning flock/herd). The 'e' spelling represents older English orthography.
Medieval and early modern English had tons of spelling variation—you'd see 'agregation,' 'aggregation,' and 'aggregacion' in different documents. Standardized spelling is actually quite recent; before the 1800s, consistency was rarely expected or achieved.
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