be in or move into a sloping position

he leaned back in his chair

she leant forward and whispered conspiratorially

a line of palm trees leaning in the wind

(of a person or animal) thin, especially healthily so; having no superfluous fat

his lean, muscular body

offering little reward, substance, or nourishment; meagre

the lean winter months

keep a small reserve to tide you over the lean years

(of a vaporized fuel mixture) having a high proportion of air

lean air-to-fuel ratios