In a level, flat, or even manner; straightforwardly or directly; possibly describing motion downward in an even way.
From 'even' (level, fair, straightforward) + 'down.' A dialectal or archaic adverbial compound, though exact etymology and usage are difficult to verify in modern sources.
Compound adverbs like this show how speakers experiment with combining directional words ('down') with descriptive ones ('even') to express precise manners of action—most don't survive, but they reveal English's generative flexibility.
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