Avuncular: 1. Literally, relating to an uncle. 2. Figuratively, suggestive of an uncle, as in geniality. 3 In medical genetics, pertaining to an aunt or uncle. An avuncular relationship is the genetic relationship between aunts and uncles and their nieces and nephews. From the Latin avunculus, meaning maternal uncle. The feminine equivalent of avuncular is materteral (like an aunt).