桅 alone means 'mast' but is most commonly seen in the compound 桅杆 (wéigǎn), which is the full word for ship's mast. The standalone character 桅 is rare outside literary or classical texts.
Left tree radical — pictograph of a trunk with branches and roots. A ship's mast is just a tall straight pole of timber, so the wood radical anchors 桅 firmly in the lumber family alongside 板, 柱, 杆, 枝.
Right 危 carries the sound wēi → wéi with a mild tone shift. It also adds a vivid semantic flavour: 危 means 'precariously high,' and a mast is exactly that — a perilously tall wooden pole swaying above the deck. Same phonetic in 跪, 诡.
