swell, get fat, thick
膨 centers on expansion in size or volume: swelling up, becoming fat, or growing thick. The idea is something filling out or puffing up from within.
膨 combines ⺼ (flesh/body) with 彭, which likely contributes the sound ボウ and the idea of swelling or bulging. The exact historical development of 彭 is uncertain, but the combination suggests bodily expansion.
The flesh radical ⺼ on the left and the bulging shape of 彭 on the right suggest a body part puffing up. Imagine a swollen ankle or a fattening belly expanding outward.
For ボウ, picture a bow (as in bow and arrow) bending and swelling under tension: bow -> ボウ, and the bent bow looks like it is swelling with stored energy.
to expand; to swell (out); to get big; to become inflated
huge; vast; enormous; colossal; extensive; large
expansion; swelling; increase; growth
to swell (out); to expand; to be inflated; to distend; to bulge
to swell; to expand; to inflate; to bulge
swelling; bulge; puff
distention; fullness; inflation; flatulence
round-faced
expansion of credit; inflation of credit
inflatable (in the sense of "can be inflated")
to look displeased; to flare one's nostrils
if you don't speak your mind, you'll feel uneasy afterwards
to make (someone's) imagination go wild; to inspire (someone's) imagination
rise
thermal expansion
thermal expansion coefficient
bundling up (in layers of clothes)
to be thickly clad
linear expansion
coefficient of linear expansion