lightly, trifling, unimportant
軽 centers on a lack of weight or seriousness: something physically light, trivial, or unimportant.
軽 is the modern simplified form of 輕. The older form combines 車 (vehicle) with 巠, which likely contributed the sound and the idea of lightness. The modern right side 圣 is a simplification.
A vehicle 車 that is light enough to be carried by a person 圣 is truly lightweight and unimportant.
For ケイ, imagine a light kayak (ケイ) so light that a car 車 can carry it easily.
light (i.e. not heavy); feeling light (i.e. offering little resistance, moving easily)
carefree; buoyant; lighthearted; sprightly
light (e.g. aircraft, truck)
abatement; reduction
easy; simple; informal; offhand; cheap
light weight
light motor vehicle (up to 660cc and 64bhp); k-car; kei car
contempt; scorn; disdain; despising; looking down on; slighting
making light of; thinking little of; slighting; belittling; dismissing; contempt; disdain
rash; thoughtless; careless; hasty; imprudent
light (of movements); nimble; sprightly; springy
minor injury
light meal; snack; refreshments
light; easy; non-serious; minor
frivolous; flippant; superficial; shallow; trifling; insincere
agile; nimble; light (of foot)
diesel oil; diesel fuel; gas oil
lightly; easily; carelessly
light music; popular music
light and easy; lambent; clever; witty; smart
thoughtless; rash; hasty; imprudent
light industry
weak earthquake