also edge-ways, "with the edge turned forward or toward a particular point," 1560s, from edge (n.) + way (n.). First attested form of the word is edgewaie; the adverbial genitive -s appears by 1640s. Edgewise (1715) appears to be a variant, based on otherwise, etc. See edge (v.).
As if it were possible for any of us to slide in a word edgewise! [Mary Mitford, "Our Village," 1824].
To edge in a word in this sense is from 1680s.
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Definitions of edgewise from WordNet
with the edge forward or on, by, or toward the edge;