However still, I’ll be happy to explain the Slavic word “what”:

It is чьто / čĭto /  ⰝⰠⰕⰑ

Originally the “č” was pronounced, however, after the drop of the yers, it became что/čto, and, because “t” is found after it, the “č” softened to “š”…

Russians today still write it as “что” (čto), however they pronounce it as što. The rest of us write it with a ш/š:
“што/što” in Belorussian, “BCSM” (Bosnian-Croatian-Serbian-Montenegrin) and Macedonian – also in Bulgarian, but they write the digraph “шт” as a single letter: “щ” – so it’s written as “щo” in Bulgarian.

(in BCSM, also the form “šta” exists – but the change from “o” to “a” is extreeeemely common. Most of you have already heard of “Akanye” which is present in Russian, Belorussian, Slovenian, etc. – however that’s not the only case of o->a ; it happens in many more cases, in many more regions and languages and dialects: “rob->rab” ; “voskrs->vaskrs” ; “vospitanie->vaspitanie” etc. and što->šta is just one more of them)

Ukrainians write is as “щo” as well (just like Bulgarians), however, they pronounce “щ” as “šč” – so it’s “ščo” there…

Also, it’s believed that actually чьто was formed from чь+то (Proto-Balto Slavic: *ki+*to) and that чь on it’s own meant “what”, while the –то was a particle… Some even in modern times use the shorter form, where they vocalize the small yer (such as the BCSM: “ča” – note that it’s “č” and not “š”, because there is no reason for it to soften to š, since there is no “t” – there are also forms “ša” and “šo” present in modern South Slavic languages, however they are modern creations, modern shortenings of “šta/što”)

So… чьто was used in this form in Eastern and Southern Slavic languages, however the characteristic of the Western Slavic languages is the usage of the Genitive form “чьсо” (čĭso), instead of the Nominative…. after the drop of the yers, it became čso, and because č and s can’t stand together side by side, Slovaks have made an elision of the “s” and turned it into “čo”; while the rest (Czechs and Poles) created a “c” by merging č and s – therefore in modern Czech ad Polish languages, it’s said: co.

So, there you have it.. the standard Slavic word for “what” is “čĭto”, however, it’s not the only word for “what” – “what” was also created with an another construction: *kъ+*jь – namely, both къто and чьто were interrogative pronouns, however, чьто was inanimate (“what”), while къто was animate (“who) – къто was formed in the same way as чьто (къ+то) – and it seems that adding the suffix -то to these root words made them interrogative, however, by adding the suffix -*jь (meaning “him”, or in this context “one”) it’d make them determiners къіи and чии (“which” and “whose” but more literally like “what one”, “who’s one”) – Slovene and Kajkavian: “kaj”, but apparently also “ki” seem to come from къіи (by the vocalization of the big yer)…

Also, another thing which I’m sure everyone who.. hmm.. speaks a language.. knows that semantic changes are also very common along with vocal changes in languages… So, the word: каковъ (actually, more specifically, the neuter gender form: каково), originally meaning like “what kind (of)” – was used to mean simply “what”, and in present day Bulgarian, and some other dialects of certain South Slavic languages, kept being in use as the only word for what, shortened to какво, or even more extreme: кво. :smiley: