[SUB- I.]
I. 1. That which lies immediately below the surface, e.g., the subsoil.
1778. [W. Marshall], Minutes Agric., 12 Dec. 1776. Rough harrows, which tore up the plits, and shook still more of the seed down to the sub-surface.
1884. H. Spencer, in Contemp. Rev., July, 31. The will of the majority is valid respecting the modes in which … parts of the surface or subsurface, may be utilized.
2. Math. In five-dimensional geometry, a three-dimensional continuum.
1873. Cayley, Math. Papers (1896), IX. 79, note. In explanation of the nomenclature [sc. five-dimensional space], observe that in 5 dimensional geometry we have: space, surface, subsurface, supercurve, curve, and point-system, according as we have between the six coordinates 0, 1, 2, 3, 4, or 5 equations.
II. as adj. [see SUB- 1 e.] Existing, lying or operating under the surface (as of the earth or water).
1875. Croll, Climate & Time, App. 553. Subsurface-water, or the stratum immediately below it.
1885. L. Oliphant, Sympneumata, 101. The subsurface world.
1888. Athenæum, 18 Aug., 215/1. Sympneumatic and subsurface consciousness.
1894. Q. Rev., April, 371. They are abundant in all surface and subsurface waters.
1894. Geol. Mag., Oct., 466. The downward creep of the surface and sub-surface soil.
1900. Pop. Sci. Monthly, March, 533. Where sewers and subsurface pipes have not yet been laid.
1902. Westm. Gaz., 31 Dec., 6/3. The construction of sub-surface torpedo boats.
