This isn’t real word though, just an (admittedly old) meme.

Longest Polish word that is in official dictionary is “pięćdziesięciogroszówka” (50 groszy coin, half of 1 PLN) - 23 letters

Of course it’s not that simple because in Polish the numerals can be joined and can be much longer, for example “dziewięćsetdziewięćdziesięciodziewięcioipółletni” (999,5 years old) - 48 letters.
And if somebondy wants to talk about their really distant ancestors (nobody do though, at least not in such manner), we could pile up the “pra” (grand) prefix to infinity creating prapraprapraprapra[…]dziadek.