Source : Webster's Revised Unabridged Dictionary (1913)

   {Opus incertum}. [L.] (Arch.) See under {Incertum}.

Incertum \In*cer"tum\, a.
   Doubtful; not of definite form.

   {Opus incertum} (Anc. Arch.), a kind of masonry employed in
      building walls, in which the stones were not squared nor
      laid in courses; rubblework.