strong-willed - это скорее "решительный, настойчивый, упрямый" и т.д. То есть качества, которые требуют присутствия силы воли, но не являются силой воли, как таковой.

Это именно "обладающий сильной волей". См.: http://www.thefreedictionary.com/strong-willed. Это Вы минус поставили?

Not really! How about these: http://www.oxforddictionaries.com/us/definition/american_english/strong-willed
http://learnersdictionary.com/definition/strong%E2%80%93willed
https://www.vocabulary.com/dictionary/strong-willed

I have as much trust in the free dictionary, as in urban dictionary - None.

And yes, dislike is from me.

This definition is from www.vocabluary.com: "Someone strong-willed doesn’t give up easily. A strong-willed person is determined.
Your will is your desire or drive to do something, so a strong-willed person is someone with a powerful will"

http://www.collinsdictionary.com/dictionary/english/strong-willed

To make it easier. Every strong -willed person is a person with a strong will, but not every person with a strong will is strong -willed.

"strong-willed" has 2 meanings: 1. with a strong will, determined 2. stubborn