Resembling or characteristic of fainting; inclined to faint; somewhat faint or weak.
From 'faint' plus the informal or colloquial suffix '-y' (having the quality of, full of). This suffix is productive in English, especially in informal speech, creating adjectives like 'cloudy' or 'sticky'.
The '-y' suffix is one of the oldest in English and is still wildly productive in modern speech—kids naturally say 'sticky' and 'yucky' without being taught, so 'fainty' would be an intuitive informal way to describe something faint-like.
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