saccule

noun

Etymology: Borrowed from Latin sacculus (“a little sack or bag”), diminutive of saccus (“a bag, sack”). Doublet of sacculus.

1. A small sac, pouch, or cyst.
2. The smaller of the two fluid-filled sacs forming part of the labyrinth of the inner ear (the other being the utricle). It contains a region of hair cells and otoliths which send signals to the brain concerning the orientation of the head.