"Adorable" is the best 'one word' translation I've ever come up with, though reading
0utf0xZer0's post is the most informative in what the word means. Unfortunately, we seem to have a faction of non-Japanese anime fans that obstinately insist on spreading confusion - their reasons vary from well-intentioned misinformation on their part to intentional dislike for plot elements they associate with the term. Sometimes, its like hearing someone insist '
tsunami' means
lunar tidal cycles over and over and over, month after month after ...
it gets hard to stay civil in the face of fundamental error.
edit: on the remote chance a few readers are not quite clear on what "adorable" means:
http://www.merriam-webster.com/dictionary/adorable