An Etymological Dictionary of Astronomy and Astrophysics

1. In 3D → magnetic reconnection models of solar plasma, a field line crossing the → fan at the
   → magnetic null point. See also → fan (Lau & Finn. 1990, ApJ 350, 672; Parnell et al. 1996, Physics of Plasmas 3, 759).
   

2. A very narrow line of light extending back from the coma into the tail of some → comets.

Etymology (EN): M.E., from O.Fr. espine, from L. spina “backbone,” originally “thorn, prickle,” cf. L. spica “ear of corn,” O.N. spikr “nail;” from PIE *spei- “sharp point.”

Etymology (PE): Xâr “spine, thorn,” related to xal-, xalidan “to prick, to pierce,” xâridan “to scratch, itch;” Av. x^vara- “wound, sore.”