To look angry, sullen, or threatening. See Synonyms at frown. To appear dark or threatening, as the sky. A threatening, sullen, or angry look. A dark and ominous look: the lower of thunderheads. Below another in rank, position, or authority. Physically situated below a similar or comparable thing: a lower shelf. Geology & Archaeology Relating to or being an earlier or older division of the period named. Biology Less advanced in organization or evolutionary development. Denoting the larger and usually more representative house of a bicameral legislature. To let, bring, or move down to a lower level. To reduce in value, degree, or quality. To weaken; undermine: lower one's energy. To reduce in standing or respect. To move down: Her hand lowered. To become less; diminish: The temperature has lowered gradually this month.