cat·kin (kăt’kĭn) A usually dense, cylindrical, often drooping cluster of unisexual apetalous flowers found in willows, birches, and oaks. Also called ament. Willow – Catkin


but·tress (bŭt’rĭs) Supported against strain in any direction by a conspicuous ridge-like enlargement of the trunk vertically to the roots. Several of these buttresses often give a tree a square appearance.