Perhaps frail and weak
Yes, probably more so than mere "thin".
brittle
skinny
The Latin word for "thin" is tenuis.
The word "fin" has the same pronunciation as the word "thin."
Scrawny means very thin; skinny and bony. TO BE THIN
The French word for "thin" is "mince".
The pair word is 'thin': thick and thin.
Yes, puny is a connotation, and it is a negative connotation because it gives off a negative effect and makes you think negatively. :)
anorexic, stick, or gangly
Emaciated is a synonym of thin that carries the most negative connotation, suggesting extreme thinness often due to illness or malnutrition.