slim
Dainty and diminutive are synonyms for small and delicate. It begins with the letter d.
Dainty.
slender
thinner
Slim.
thinner
The four-letter word for thin and narrow, not wide or thick, is "slim." "Slim" describes something that is slender or slight in form, emphasizing a lack of excess bulk. It is commonly used to describe objects or people that are trim or delicate in appearance.
The word is slim.
Slender?
dainty
slim lean or thin