dawn
旴 centers on the first light of day: dawn. It is a rare character whose meaning is tied to the early morning sun.
旴 combines 日 (sun) with 于, which likely contributes a phonetic element. The exact historical development is uncertain, but the sun component clearly ties it to dawn.
The sun 日 rises beside 于, like the first ray of dawn peeking over the horizon. Picture the early morning light breaking through.
For ク, imagine the cool (クール) air of dawn: cool -> ク, and the sun rises into the cool morning sky.