What is 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 called?

incertum — 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. (Webster's 1913.)