Japanese note

Not in any textbook, but I've so far noticed:

話す hanasu "to talk"
話し hanashi "conversation"

写す utsusu "to copy"
写し utsushi "copy"

写る utsuru "to be photographed, to be projected"
写り utsuri "image, projection"

So it seems that swapping the final -u to a -i turns the verb into a result-type noun. (The result of talking is a conversation, the result of copying is a copy, etc.) Japanese derivational morphology is incredibly well hidden by the fact they pasted Chinese characters all over their language – there's a few words I've spotted where multiple roots get the same kanji, and where one of the roots has its meanings split between two different kanji due to Chinese splitting the concept space differently – but it is there. And I will find it.

(quick phone ETA - wrt "root split between kanji" I mean frex
帰る kaeru "to return"
返す kaesu "to return (sth)"