The Collaborative International Dictionary of English v.0.48:

Stirps \Stirps\, n.; pl. Stirpes. [L., stem, stock.]
   1. (Law) Stock; race; family. --Blackstone.
      [1913 Webster]

   2. (Bot.) A race, or a fixed and permanent variety.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "stirps":
   affiliation, animal kingdom, apparentation, birth, blood,
   bloodline, branch, breed, brood, clan, class, common ancestry,
   consanguinity, deme, derivation, descent, direct line,
   distaff side, extraction, family, female line, filiation, folk,
   gens, house, kind, line, line of descent, lineage, male line,
   matriclan, nation, order, patriclan, people, phratry, phyle,
   phylum, plant kingdom, race, seed, sept, side, spear side, species,
   spindle side, stem, stock, strain, succession, sword side, totem,
   tribe