Dineen p.890:

Réilteach (-teannach), réilteann (a star, but esp. fig., a fair lady). See réaltach, réalta.

P.884 gives us:

Réalta, -n, -tainne, d. -ain, pl. id. and -tana, f., a star, the figure of a star, a mark on the forehead of a beast; fig. a fair lady; r. na maidne, the morning star, fig., a sweetheart; r. an mhadraidh, the dog-star; r. eolais, the Pole-star, a guiding star, a lover; r. oighridh, a frost-bright star, r. seaca, id.; r. na scuaibe, a comet (Conem.), r. an earbaill, r. mhongach, id.; R. na bhFileadh, the Star of the Poets, the building (Teach Miodhchuarta) at Tara frequented by bards and brehons; al. réalt (g. -éilte), réilteann (g. -tinne), réilthín, réaltann (g. -tainne); Old Ir. rétglu, Mid. Ir. rétlu.