to commence, to found, to devise, at first, to originate, to strike
肈 centers on the act of beginning or setting something in motion: commencing, founding, devising, or originating. The meaning 'to strike' extends this idea to initiating a forceful action.
肈 is a rare character whose exact historical development is uncertain. It visually contains 聿 (a hand holding a brush) and other elements, but the original composition and how it came to mean 'commence' or 'strike' are not clearly established.
The bottom component 聿 looks like a hand holding a brush, ready to make the first stroke. Picture that first stroke as the moment something begins: a plan is devised, a foundation is laid, or a strike is launched.
For チョウ, imagine a chief named Chou who always commences projects with a decisive strike of a brush: Chou -> チョウ, and his first stroke starts everything.