I think that one word does not capture it. However, I have heard of the one word that is it's opposite: FEAR. That would imply that if you are constantly fearful, it would be very hard to feel love. As to what love IS, I think it can be many things: gratitude, appreciation, forgiveness, positive energy, passion, joy, empathy, compassion, acceptance. I think that if one can bring these things into their life, they will experience love. But i think the prerequisite is that you direct these things towards yourself as well as others. If you leave yourself out, it won't work.