lacuna

‖n.; pl. L. Lacunæ E. Lacunas [ L., ditch, pit, lake, orig., anything hollow. See Lagoon. ] 1. A small opening; a small pit or depression; a small blank space; a gap or vacancy; a hiatus. [ 1913 Webster ]

2. (Biol.) A small opening; a small depression or cavity; a space, as a vacant space between the cells of plants, or one of the spaces left among the tissues of the lower animals, which serve in place of vessels for the circulation of the body fluids, or the cavity or sac, usually of very small size, in a mucous membrane. [ 1913 Webster ]

{ } a. Pertaining to, or having, lacunæ; as, a lacunar circulation. [ 1913 Webster ]