Perhaps frail and weak
A negative word for "thin" is "scrawny," which often implies an unhealthy or unattractive lack of body mass. Other terms like "emaciated" can also convey a similar negative connotation, suggesting extreme thinness due to malnutrition or illness. These words typically carry a judgment about the undesirable appearance or health implications of being thin.
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