An Etymological Dictionary of Astronomy and Astrophysics
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A population of relatively small (typically < 2°) → high-velocity clouds, which are spatially and kinematically isolated from the gas distribution in their environment. They are thought to be located in the → intergalactic medium of the → Local Group.

→ compact; → high-velocity cloud.

A population of neutral or partly ionized gas clouds in the → Galactic halo which are seen as high-altitude structures in the atomic hydrogen 21 cm emission at high radial velocities (v_LSR> 100 km/sec). They have substantial neutral column densities (> 10¹⁹ cm^-2) and their metallicities range from 0.1 to about 1.0 times solar. The distances to the majority of them remain unknown. They may represent the continuing infall of matter onto the → Local Group. See also → compact high-velocity clouds.

→ high; → velocity; → cloud.

Abr, → cloud; tondrow "fast moving," from tond "fast," → speed; row, present stem of raftan "to go, walk; to flow" (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").