luxuriance
矗 centers on abundant, upright growth: a sense of luxuriance, with things standing tall and thick together.
矗 is a triple repetition of 直 (straight), visually emphasizing things standing straight and tall in abundance. The exact historical development is uncertain, but the character likely uses reduplication to intensify the idea of uprightness and luxuriance.
Three 直 (straight) components stacked together: imagine a dense forest of tall, straight trees growing luxuriantly.
For チョク, picture a straight, upright chock of wood holding back a lush, overgrown garden: chock -> チョク, and the triple 直 reinforces the straight, abundant growth.