The posting below by Professor W. Sundermann’s discussion of the Arteshdar of the Sassanian army was orginally published in the Encyclopedia Iranica on December 15, 1986 (last updated by Iranica on August 15, 2011).
ARTĒŠTĀR (Middle Persian), a learned calque on and translation of the Avestan raθaēštā “warrior, war-hero” (Bartholomae, AirWb., col. 1506), which is a -tar formation, based on an original raθaēštā, literally: “in chariot standing, i.e. charioteer” (J. Kellens, Les noms racines de l’Avesta, Wiesbaden, 1974, pp. 231f.). This explanation of the Avestan forms is supported not only by the existence of the Sanskrit word ratheṣṭhā “charioteer” but also by the proper name Ratešda appearing in the Persepolis tablets, which must be its Old Persian equivalent (see M. Mayrhofer, Onomastica Persepolitana, Vienna, 1973, no. 8.1423). In the Middle Persian form, the long ā of the last syllable can be derived either from the accusative or from a secondary thematicization of the tar- stem (see Kellens, loc. cit.); and the initial a is attributed to analogy with artīk “fighting” by H. S. Nyberg (A Manual of Pahlavi II, Wiesbaden, 1974, p. 30, and Hilfsbuch des Pehlevi II, Uppsala, 1931, p. 2). The reading artēštār (with art- rather than arat-) is supported by New Persian artēšdār “soldier” (“miles” in J. A. Vullers, Lexicon Persico-Latinum I, repr. Graz, 1962, p. 76), though aratištār is found in Pāzand (Nyberg, Manual, loc. cit.), and ratēštār, which is nearer to the Avestan form, appears in the Pahlavi translation of the Avesta (B. N. Dhabhar, Pahlavi Yasna and Visperad, Bombay, 1949, p. 107; D. D. Kapadia, Glossary of Pahlavi Vendidad, Bombay, 1953, p. 268). If Nyberg’s theory is correct, the word artēštār must have been invented before the form of the word for “fighting” changed from artīk to ardīg, i.e. before the Sasanian period. The form nīsārīān in the Šāh-nāma (F. Wolff, Glossar zu Firdosis Schahname, Berlin, 1935, p. 832) was emended by E. Benveniste to artēštārī (“Les classes sociales dans la tradition avestique,” JA 221, 1932, p. 133).
Having entered the New Persian language in the form artēšdār (metrically artēšadār) or similar variants, the word was misunderstood as “artēš-having” (with -dār from dāštan “to have”).
The Farhangestān (Iranian Academy) established in Reżā Shah’s reign was misled by this misinterpretation of “artēš-dār” to see in the first component a Persian word arteš meaning “army.” This solecism was officially approved, and the Iranian army has been called the arteš ever since (Bozorg Alavi, Geschichte und Entwicklung der modernen persischen Literatur,