Skinny means thin in a way that looks like too little, with the bones showing at the wrist and shoulder. The kid whose jeans need the belt pulled to the last hole.
It is not a compliment. Slim and slender are kind, thin is neutral, and skinny suggests something is missing, so it stings even when you meant it warmly. The word has spread to objects: skinny jeans that grip the leg, a skinny tie, a skinny latte made with skimmed milk. Skinny-dipping is swimming with nothing on. And in American speech, the skinny is the inside information — give me the skinny on the new boss.
1adjectiveskinnyVery thin, in a way that suggests too little flesh.
“He was a skinny boy who grew into a broad man.”
informal in this meaning — an editor’s judgement
2adjectiveclothesOf clothes: cut very close to the body.
“She wore skinny jeans and heavy black boots.”
3adjectivedrinkOf a drink: made with skimmed or low-fat milk.
“A skinny latte, please, and nothing to eat.”
Also accepted in games: thin
In Middle English, skinny meant simply resembling skin: skin with -y stuck on the end. The sense of having too little flesh probably grew out of the phrase skin and bones, and the naked sense in skinny-dipping is exactly what it says, since skin is what you are showing.
Middle English
skinny — resembling skin
English, today
skinny
From Middle English skinny (“resembling skin”), equivalent to skin + y. The meaning associated with lack of fat or muscle possibly derives from the phrase skin and bones; the meaning associated with nudity refers to the exposed skin.
Etymology from Wiktionary, CC BY-SA