An Etymological Dictionary of Astronomy and Astrophysics

1. A tall, woody perennial plant usually with a single trunk.
   

   2. Math.: → factor tree.
      

   3. A → data structure that is used to represent hierarchical data.
      

   4. In → graph theory, a → connected graph with no → cycles.
      

   5. A mathematical structure that can be viewed as either a graph or as a data structure. Many powerful algorithms in computer science and software engineering are tree based algorithms.

Etymology (EN): M.E., from O.E. treo, treow “tree, wood,” from P.Gmc. *trewan (cf. O.S. trio, O.N. tre, Goth. triu), from PIE *deru- “wood” (cf. Mod.Pers. dâr “tree;” O.Pers. dāruv- “wood;” Av. dāuru- “piece of wood, tree trunk;” Skt. dāru- “tree, wood;”
Gk. drus “tree;” Serb. drvo “tree;” L. larix “larch tree;”
Rus. drevo “tree, wood;” Pol. drwa “wood;” Lith. derva “pine wood;” O.Ir. daur, Welsh derwen “oak”).

Etymology (PE): Deraxt “tree;” Mid.Pers. draxt “tree,” two possible etymologies. A suffixed variant of dâr “tree,” cognate with E. tree, as above. Alternatively, from Av. *draxta- “firmly stood, fixed” (as in handraxta-), from drang-, dranj- “to fix, fasten, strengthen, hold,” dražaite “holds,” infinitive drājnhe; cf. Khotanese drys- “to hold;” Sogdian drγ- “to hold;” Parthian Mid.Pers. drxs “to endure.”