underdraught
nounEtymology From under- + draught.
1
A draught of air from underneath.
- I noticed, too, that small radiating walls had been built out from the central mass, on which, allowing full underdraught, had been laid the outside coating of the central pyre, in shape of fagots and lighter fuel.1887, The Cornhill Magazine, volume 9, page 158:
2
Engineering, Metallurgy, Natural sciences, Physical sciences The situation where part of a formed or cast shape has a reverse taper or inward‑leaning surface that makes it difficult to remove from the die or mold.