An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

"From the beginning," as opposed to in medias res "starting in the middle of the story." In physics and chemistry "from first principles;" → ab initio calculation.

L. "from the beginning," from ab "from," → ab- + initio, ablative of initium "a beginning, an entrance," from inire "to go into, begin," from in- "into, in" + ire "to go" (cf. Gk. ienai "to go," Skt. eti "goes," O.Pers. aitiy "goes," Av. aeiti "goes," Mod.Pers. âyad "comes," PIE *ei- "to go, to walk").

Hac bon, from Mid.Pers. hac "from" (O.Pers. hacā "from," Av. hacā "from, out of," cf. Skt. sácā "with," PIE base *sek^w- "to follow," Av. hac-, hax- "to follow," hacaiti "follows," Skt. sácate "accompanies, follows," Gk. hepesthai "to follow," L. sequi "to follow," Lith. seku "to follow") + bon "beginning, base, root" (Av. būna- "base, depth," cf. Skt. bundha-, budhná- "base, bottom," Pali bunda- "root of tree").

In physics and chemistry, a calculation that relies on basic and established laws without additional assumptions or special models. Experimental input in ab initio calculations is limited to the determination of values of fundamental physical constants.

→ ab initio; → calculation.