If you need a poetic way to say "sorrow," use the word dolor. Your sad-eyed dog might express a great deal of dolor when you leave him alone for the day.
You can use dolor to talk about heartache or sadness, like the dolor of guests at a funeral or a winter sky's gray dolor as the days get shorter. No matter how you use the noun dolor, it's going to have a poetic sound to it. It's more common to come across the adjective dolorous, or "full of sorrow." In Latin, dolor means "pain or grief."