The Collaborative International Dictionary of English v.0.48:

Stela \Ste"la\, n.; pl. Stelae. [L., from Gr. ? a post, an
   upright stone.] (Gr. Antiq.)
   A small column or pillar, used as a monument, milestone, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stela
    n 1: an ancient upright stone slab bearing markings [syn:
         stele, stela]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "stela":
   arch, barrow, boundary stone, brass, bust, cairn, cenotaph, column,
   cromlech, cross, cup, cyclolith, dolmen, footstone, grave,
   gravestone, headstone, hoarstone, inscription, marker, mausoleum,
   megalith, memento, memorial, memorial arch, memorial column,
   memorial statue, memorial stone, menhir, monolith, monument, mound,
   necrology, obelisk, obituary, pillar, plaque, prize, pyramid,
   reliquary, remembrance, ribbon, rostral column, shaft, shrine,
   stone, stupa, tablet, testimonial, tomb, tombstone, tope, trophy