Source : Webster's Revised Unabridged Dictionary (1913)

Lacunal \La*cu"nal\, Lacunar \La*cu"nar\, a.
   Pertaining to, or having, lacun[ae]; as, a lacunar
   circulation.

Lacunar \La*cu"nar\, n.; pl. E. {Lacunars}, L. {Lacunaria}. [L.]
   (Arch.)
   (a) 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
   (b) One of the sunken panels in such a ceiling.