[EN 12792:2003, 214]:diameter of a circular duct which will cause the same pressure drop at equal air velocity and equal friction coefficient than the considered (rectangular) duct

[EN 12792:2003, 215]:device that enables the value of the humidity of a sample of air or other media to be determined. 

[AIVC, Air infiltration and ventilation glossary, 1992]:the combination of two or more substances such that the parts of one are unevenly distributed among the parts of another.