clear
晰 centers on clarity and distinctness: something that is clearly visible, well-defined, or easy to perceive.
晰 combines 日 (sun, light) with 析, which likely contributes the sound and the idea of separating or analyzing, together suggesting clarity brought to light.
The sun 日 shines on something being split apart 析, making every detail clear and distinct.
For シャク, imagine a clear shack by the sea where the sun makes everything visible: shack -> シャク, and the light makes the scene clear.
clear; distinct
clear and distinct (e.g. perception, esp. in Cartesianism); having a clear head
lucid dream; dream in which the dreamer is aware that they are dreaming
terminal lucidity; end-of-life rally
being clearheaded; having a keen (sharp, brilliant) mind