light carriage, trifling, light
輶 centers on lightness in both physical and figurative senses: a light carriage that is easy to move, and by extension something trifling or of little weight.
輶 combines 車 (vehicle) with 酋, which likely contributes the sound. The character expresses a light carriage, with the lightness sense extending figuratively.
A vehicle (車) with a chief (酋) riding in it must be light and swift, like a light carriage. The idea of lightness then extends to trifling matters.
For ユウ, imagine a light carriage being pulled by a ewe (a female sheep): ewe -> ユウ, and the carriage is so light even a ewe can pull it.