When was the word enlightenment introduced into Theravada Buddhism?

I feel the word enlightenment conveys the wrong meaning if used in context of nibbana. For example, Buddha says that nibbana is similar to a lighted lamp, having taken away the oil and the wick, will not light ("as though a lamp was extinguished" Rathana Sutta - Sutta Nipatha, Chulla Waggo, 2-1, 237). I'm interested in knowing how this word was associated with Theravada Buddhism if anyone knows early references of such usage. Thanks in advance.