IPA: /ˈliːnər/
KK: /ˈlinər/
Having less body fat or being thinner than someone or something else.
After months of exercise and healthy eating, she became leaner and more fit.
Leaner → It is formed from "lean" (from Old English "hlēanian", meaning to make thin or to incline) and "-er" (meaning a person who). The word "leaner" refers to a person or thing that is thinner or more inclined than another.
Think of someone who is 'making thin' ('lean') and the '-er' just means a person. A leaner is someone who is thinner.