Weight

léger / légère = light (as in "not heavy")
lourd / lourde = heavy (the 'd' is silent in the masculine form)

Examples:
je manger léger = I eat light (léger can also be an adverb)
à la légère = lightly, not seriously, without thinking
prendre quelquechose à la légère = not to take something seriously
avoir le cœur lourd = to have a heavy heart
avoir la main lourde = to be heavy-handed
t'es lourd! = you're getting on my nerves! (slang)