Antonyms of adj underweight

1 sense of underweight

Sense 1
scraggy, boney, scrawny, skinny, underweight, weedy -- (being very thin; "a child with skinny freckled legs"; "a long scrawny neck")

INDIRECT (VIA thin) -> fat -- (having an (over)abundance of flesh; "he hadn't remembered how fat she was")

Similarity of adj underweight

1 sense of underweight

Sense 1
scraggy, boney, scrawny, skinny, underweight, weedy -- (being very thin; "a child with skinny freckled legs"; "a long scrawny neck")
       => thin (vs. fat), lean -- (lacking excess flesh; "you can't be too rich or too thin"; "Yon Cassius has a lean and hungry look"-Shakespeare)