manner (German/Faroese/Icelandic/Norwegian/Old English/Old Norse mann, Turkish er)—this one only works in the indefinite accusative.
This is quite a fun distraction; thanks, sionnach.
*Or maybe nomonyms or namonyms to fill the self-referentiality quota? If we take onym as the second form, we have French nom, and if we take nym, we have Esperanto/Ido nomo, or Old High German namo, all meaning "name".
Great pattern, sionnach! It's a bit of a stretch, but how about "dogfish", a kind of shark? In Ashkenazic Hebrew "dog" means fish and is pronounced "dawg", but it's usually transliterated "dag". In Sephardic Hebrew it's pronounced "dahg".