 A number of words in English are used metaphorically, with a meaning that is not exactly the same as their literal meaning. Usually they apply a quality of one word to another word. For example, when we say that something is lightning fast, we are using the quality of lightning, which is almost instantaneous, to describe something that is extremely fast. Another example is the root of the problem. The literal meaning of the word root is the part of a plant or tree that is under the soil. The roots are what support and sustain the entire tree. Therefore, the root of the problem is the deepest, most basic, or fundamental reason for the problem. Many metaphors are related to elements in the natural world, such as light and dark, water, fire, and plants. In this lesson, you'll learn five collocations in each category. If someone's face or eyes light up, it means that they suddenly get very happy or excited. You can also say someone's eyes are shining with delight. The expression lighten the mood means to make a depressing atmosphere or depressing situation more relaxed and happy. On the other hand, if someone's face, eyes, or expression darkens, it means that they suddenly appear sad or angry. Dark days or dark times refer to periods of time that are bad or unpleasant, full of problems. A heated discussion or heated debate is one that is very intense, often with negative emotions like anger. If someone has a fiery temper, it means that when they get angry, they get very angry and could possibly explode. There's also the expression tempers flared to describe a situation when people began to get angry. The verbs kindle and spark describe the act of starting fires. Kindle is usually used for starting positive things. Something can kindle interest, kindle enthusiasm, or kindle hope. And spark is usually used for starting negative things. Something can spark outrage or spark controversy. It's difficult for a plant to grow in soil that has a lot of rocks, so if something gets off to a rocky start, it means that it encountered many problems in the beginning. Blossomings are the small, sharp growths that appear on some plants, such as roses. The expression a thorny issue describes a matter that is difficult, complicated, and possibly dangerous. The word blossom is used to describe when a flower appears and opens, revealing all its beauty. So, if a romance or friendship is blossoming, then it is developing in a beautiful way. If your efforts begin to produce the desired results, we can say your efforts are bearing fruit. Finally, a seed represents something small that can grow into something big. So, if some event plants seeds of hope, or seeds of jealousy, it means it produces a small feeling that can grow into a stronger emotion over time. If you'd like to learn a thousand English collocations, check out the e-book and Audio 1000 English Collocations in 10 minutes a day. It will help you learn common combinations of English words and practice them with exercises, even if you don't have a lot of time to study.