seldom.
Because this word is an adverb as well as an adjective, the nonword *"seldomly" is never (not merely seldom) needed — e.g.:
o “Hogan was a man so focused that he seldomly [read ‘seldom’] noticed what was going on around him.” Jeff Babineau, “Hogan’s Legacy,” Orlando Sentinel, 3 Aug. 1997, at C4.
o “There, one obviously bored soldier checks identifications, and seldomly [read ‘seldom’] exercises his prerogative of looking inside bags and purses.” “Deadly Biowarfare Collection Amid Disrepair in Russian Lab,” San Antonio Express-News, 10 Aug. 1997, at A4.
It isn’t even listed in most dictionaries.
Language-Change Index — *"seldomly" for “seldom”: Stage 1.
*Invariably inferior forms.
For information about the Language-Change Index click here.
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Quotation of the Day: “Any work of art, provided it springs from a sincere motivation to further understanding between people, is an act of faith and therefore is an act of love.” Truman Capote (as quoted in Harvey Breit, The Writer Observed 237 (1956)).