(1):

(n.) A partition in any compartment, for various purposes.

(2):

(n.) The muscular and tendinous partition separating the cavity of the chest from that of the abdomen; the midriff.

(3):

(n.) A dividing membrane or thin partition, commonly with an opening through it.

(4):

(n.) A plate with an opening, which is generally circular, used in instruments to cut off marginal portions of a beam of light, as at the focus of a telescope.

(5):

(n.) A calcareous plate which divides the cavity of certain shells into two parts.