An Etymological Dictionary of Astronomy and Astrophysics

The region located between the → termination shock and the → heliopause where the turbulent and hot → solar wind is compressed as it passes outward against the interstellar wind.

Etymology (EN): Heliosheath, from → helio- + sheath, from O.E. sceað, scæð; cf. M.Du. schede, Du. schede, O.H.G. skaida, Ger. Scheide “scabbard.”

Etymology (PE): Hurniyâm, from hur- “sun,” → helio-,

• niyâm “sheath,” from Proto-Iranian *nigāma-, from ni- “down; into,” → ni- (PIE),
• gāma- “to go, to come” (Av. gam- “to come; to go,” jamaiti “goes;” O.Pers. gam- “to come; to go;” Mod./Mid.Pers. gâm
  “step, pace,” âmadan “to come;” cf. Skt. gamati “goes;” Gk. bainein “to go, walk, step;” L. venire “to come;” Tocharian A käm- “to come;” O.H.G. queman “to come;” E. come; PIE root *gwem- “to go, come”); cf. Skt. nigamá- “insertion, incorporation.”