An Etymological Dictionary of Astronomy and Astrophysics

Geophysics: A layer of the atmosphere or the sea, regarded as lying between horizontal planes.
Geology: A single bed of → sedimentary rock, generally consisting of one kind of matter representing continuous deposition.

Etymology (EN): From L. stratum “thing spread out, pavement,” from neuter p.p. of sternere “to spread out, lay down, stretch out,” from PIE base *ster- “to spread, extend, stretch out;” cf. Pers. gostar-, gostardan “to spread;” Av. star- “to spread,” starati “spreads;” Skt. star- “to spread out, extend, strew,”
strnati “spreads;” Gk. stornumi “I spread out,” strotos “spread, laid out;” Ger. Strahlung “radiation,” from strahlen “to radiate,” from Strahl “ray;” from M.H.G. strāle; from O.H.G. strāla “arrow,stripe.”

Etymology (PE): Ciné “layer,” from cin present stem of cidan “to collect, gather;” Mid.Pers. cyn- “to gather, collect,” Parthian Mid.Pers. (+*ni-) ncyn- “to pile up, heap up together,” nycnyšn “stack;” Av. ci- (caē-, caii-) “to heap up, gather;” cf. Skt. ci- “to gather, heap up,” cinoti “gathers.”