It is well known that clutter (spectral interference) from atmospheric constituents can be a severe limit for spectroscopic point sensors, especially where high sensitivity and specificity are required. In this paper, we will show for submillimeter/terahertz (SMM/THz) sensors that use cw electronic techniques the clutter limit for the detection of common target gases with absolute specificity (probability of false alarm $\ll {10}^{-10}$ ) is in the ppt (1 part in ${10}^{12}$ ) range or lower. This is because the most abundant atmospheric gases are either transparent to SMM/THz radiation (e.g., ${\mathrm{CO}}_2$ ) or have spectra that are very sparse relative to the ${10}^5$ Doppler-limited resolution elements available (e.g., ${\mathrm{H}}_2\mathrm{O}$ ). Moreover, the low clutter limit demonstrated for cw electronic systems in the SMM/THz is independent of system size and complexity.