1.
master carpenter, master builder
The head carpenter who leads a construction project, supervising and coordinating the work of other carpenters. A title of skill and authority in the traditional building trades.
2.
leader, chief, head
By extension, a leader or head of a group. Used historically for clan leaders and heads of organizations.
Usage
In modern usage, sense 1 (master carpenter) is most common. When someone says 棟梁 today, they typically mean the head carpenter on a construction project. The word carries a sense of traditional craftsmanship and authority. Sense 2 (leader) is mainly encountered in historical contexts, particularly in reference to the heads of warrior clans during the medieval period.