Microseism
Pronunciation : Mi"cro*seism, n. [Micro- + Gr. an earthquake
Part of Speech : fr.
Definition : Defn: A feeble earth tremor not directly perceptible, but detected only by means of specially constructed apparatus. -- Mi`cro*seis"mic (#), *seis"mic*al (#), a.
to shake.]
Source : Webster's Unabridged Dictionary, 1913