Which came first: いや (the interjection), or 嫌がる and similar words? I assume that the interjection is cognate with a bunch of other words beginning with _iya-_ such as , perhaps via the semantics of 'disagreeable'. But did the interjection come first and get lexicalised into verbs and adjectives? Or does the interjection _derive_ from the other forms? Which is the earlier form?

According to the entry of in :

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The interjection sense first appears in 1254:

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And the adjective in 1477:

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It suggests that the adjective usage of (with all its derivation) is a secondary development.

While derives from an older form in the middle ages, dates back to , that means those two are not cognate.

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As an aside, also generated a derived verb, namely > "deny, negate", which has been widely used till now.