underswell means an undercurrent. Lexicurio rates it Sui generis — a strength score of 87 out of 100.
Etymology
From under- + swell.
noun
- An undercurrent.
- A swelling undersection.“Something had altered the normal perspectives of the room. Trying to focus on the grey underswell of the ceiling, I listened for footsteps outside. Sure enough, the corridor wall began to retract.”