In a manner relating to or characterized by blindness.
From ableptical + the adverbial suffix '-ly'. This adverb form allowed 17th-19th century medical writers to describe how something occurred in the manner of blindness or sightlessness.
English lets us stack suffixes endlessly—take 'blind,' add '-ness' for blindness, add '-ic' for relating to it, add '-al' to make it an adjective, then '-ly' for an adverb. Medieval scholars would have loved this productivity!
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