big
俁 centers on largeness or bigness, describing something of great size or stature.
俁 combines 亻 (person) with 吳, which likely contributes the sound and may relate to the idea of bigness, but the exact historical development is uncertain.
A person 亻 beside the large, sprawling shape 吳 suggests someone of imposing size: 俁 means big.
For グ, imagine a big, gooey blob expanding beside the person: goo -> グ, and its bigness is overwhelming.