inflood comes from in- ('in') + flood, from Old English flod ('flowing water, deluge'), from Proto-Germanic *floduz, from a Proto-Indo-European root *plew- ('to flow, swim'). Morphologically, the prefixed shape matters: the initial element belongs to the recorded formation and helps explain the modern form's surface analysis. In present English, the noun sense is "a flowing in; an influx or inundation", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as flood, inflow, and influx. Its semantic neighborhood includes influx, inflow, inrush, and inundation, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Old English flod, Proto-Germanic *floduz, and Proto-Indo-European *plew-.