Perhaps frail and weak
Yes, probably more so than mere "thin".
brittle
skinny
The Latin word for "thin" is tenuis.
Scrawny means very thin; skinny and bony. TO BE THIN
The word "fin" has the same pronunciation as the word "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.