without, apart from, none, a negative
橆 centers on absence or negation: being without something, apart from it, or expressing a negative. The idea of 'none' is the core, with other meanings as natural extensions.
橆 is a variant or older form of 無, which originally depicted a person with ornaments or dancing, later borrowed for 'not have'. The addition of 林 may be a later development, but the exact historical relationship is uncertain.
The bottom 林 (grove) is dense, but the upper part suggests something missing or negated. Imagine a grove where everything is absent—no trees, no sound—just a negative space.
For ブ, picture a 'boo' sound of negation: when something is without value, you say 'boo'—ブ cues the negative meaning.