Turkish; Why “Yazın” and not “Yazda”

Turkish language says "Yazın" for "during the summer" instead of "Yazda". But why?

In Turkish, when we want to indicate an action performed "with" or "by means of" something, we use the word ile (meaning "with") along with a specific suffix which varies depending on the context. For example, "Arabayla geldi" means "he came with (by the use of a) car."

However, in the distant past of Turkish, there was a different way to convey this idea, involving a suffix -n aka the old instrumental case. This older method still lingers in some words like "yazın" ("during the summer"), "kışın" ("during the winter"), "öğlen" ("at noon"), and "yayan" ("by foot," "on foot").

Over time, the use of this -n suffix became less common in Turkish, and this is where the word "ile" comes into play. "İle" expanded its meaning from simply "with" to functioning as an instrumental marker, indicating how something is done.

When you encounter "yazın" in Turkish, you're witnessing a piece of the language's fascinating linguistic evolution.