What is "lacunar"

Lacunal \La*cu"nal\ (l[.a]*k[=u]"nal), Lacunar \La*cu"nar\ (l[.a]*k[=u]"n[~e]r), a. Pertaining to, or having, lacun[ae]; as, a lacunar circulation.

Lacunar \La*cu"nar\, n.; pl. E. Lacunars (l[.a]*k[=u]"n[~e]rz), L. Lacunaria (l[a^]k`[-u]*n[=a]"r[i^]*[.a]). [L.] (Arch.)

1. The ceiling or under surface of any part, especially when it consists of compartments, sunk or hollowed without spaces or bands between the panels.
   --Gwilt

2. One of the sunken panels in such a ceiling.

a. (context medicine English) Of or pertaining to a lacuna n. (context architecture English) A coffer; a ceiling constructed of coffers