a person who is dieting to lose weight

a super slimmer who lost almost ten stone

(of a person or their build) gracefully thin; slender

her slim figure

the girls were tall and slim

(of something abstract, especially a chance or margin) very small

there was just a slim chance of success

a slim majority of sixteen

crafty, sly, or unscrupulous

make oneself thinner, especially by dieting

if he's overweight, he should slim