thin, skinny, low-fat, lean
She was terribly thin.
Il lui est difficile de vivre de sa maigre retraite.
It’s difficult for him to live on his meager pension.
Être grand et maigre permet de mieux dégager la chaleur dans les climats chauds.
Being tall and thin helps the body dissipate heat more effectively in hot climates.
— The Man from Earth (2007)
Ziri devenait de plus en plus maigre et faible.
Ziri was becoming increasingly thin and weak.
Ben en attendant, tu ferais mieux de soigner ta couche maigre.
Well, in the meantime, you'd better take care of your thin layer.
— Le Fabuleux Destin d'Amélie Poulain (2001)