The act or condition of being deprived of sight; blindness or loss of vision.
From desight (to deprive of sight) plus -ment (a noun-forming suffix indicating an act, condition, or result). Follows English patterns for turning verbs into abstract nouns.
This word is almost entirely obsolete now, but it demonstrates how thoroughly English once tried to use '-ment' suffixes—we have 'amazement,' 'bewitchment,' but 'desightment' never caught on, probably because 'blindness' was already the standard term.
Complete word intelligence in one call. Free tier — 50 lookups/day.