Full of faintness; prone to fainting or characterized by faintness; timid or cowardly.
From 'faint' combined with the suffix '-ful' (full of, characterized by). This construction is typical in Middle and Early Modern English, though the word is now archaic.
English speakers used to add '-ful' to almost any word to mean 'full of that quality,' which is why we see archaic adjectives like 'faintful' and 'sorrowful'—but 'faintful' sounds so dramatic that it never quite caught on in modern usage.
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