Definition of stillstand:
(v) :
(geology) To cease in either glacial advance or retreat.
(n) :
(geology) A period of time during which the terminus of a glacier remains stationary.
(n) :
(geology) A period of geologic time during which eustatic sea level stays apparently constant, relative to adjacent periods of geologic time, neither characterized by transgression, nor regression.
(n) :
(obsolete) A standstill.