The title says it all really: what is the etymology of JK Rowling's word 'Muggle'?
I have read from the Harry Potter Wikia that:
Muggle is derived from the word "mug," which refers to a gullible person. J. K. Rowling has commented that she added a syllable to soften the word, which she wanted to suggest "both foolishness and lovability." In the Brazilian translation of the series the term "muggle" was adapted to "trouxa", which literally means "fool", albeit not necessarily lovable at all.
However there is no citation to confirm the reliability of this. I am looking for a quote from JK Rowling which confirms (or refutes) this.