The meaning of the Persian name Rostam (or Rustam) is indeed somewhat uncertain, but after some extensive googling, it seems that the meaning of the name is generally related to one or more of the following:- braveness, boldness (see Avestan 'takhma' or 'taxma' meaning "brave, valiant", which is an element in the Persian names Tahmasp and Tahmuras in the main database); - strength (see Pahlavi 'stahm' meaning "power" on page 77 of "A concise Pahlavi dictionary" written by D. N. MacKenzie); - tallness (or big in size, or even growth); - freedom ("I am freed"); - a river.For more information, see the following sources (along with quotations) that I had come across:- https://en.wikipedia.org/wiki/Rostam#Background (in English): "the etymology of the name Rostam is from Raodh+Takhma, where Raodh means "growth, reaped, developed" and Takhma means "brave". In the Avesta, the form is *Raosta-takhma and in Pahlavi *Rodastahm. Mehrdad Bahar regards the etymology of the name to be "Ruta-staxma", i.e. the river that descends, and argues that Rostam could have been an ancient god of the river Helmand."- http://www.plsn.ir/wp-content/uploads/2016/11/Rostam.pdf (in English): this is a 4-page PDF file that contains the same information as the Wikipedia article above.- https://ru.wikipedia.org/wiki/%D0%A0%D1%83%D1%81%D1%82%D0%B0%D0%BC (in Russian): mentions that the Pahlavi form can be both Rodastahm and Rostahm and that the name is ultimately derived from Proto-Iranian "Raudas-taxma".- https://www.nordicnames.de/wiki/Rustan (in English): "derived from Middle Persian 'rôtastahm' meaning "enormously tall, very big".- http://quranicnames.com/rustam/ (in English): "Rustam is a Persian name for boys that means "tall", "strong", "hulk-like"."- http://quranicnames.com/meaning-of-rustam-persian-boy-name/ (in English): "Rustam is a Persian name for boys. It is the name of an ancient Persian hero who was known as the strongest person in Iran. His name means "strongly-built"."- http://www.avesta.org/znames.htm (in English): "Name of the celebrated hero of Iran; strong and well built; Pahl. Rotastahm; "I am freed". The words spoken by Rustam's mother at his birth, for he was the size of a one-year-old."- see page 381 of "The Complete Book of Muslim and Parsi Names" written by Maneka Gandhi and Ozair Husain: https://books.google.nl/books?id=SSdCL2ZfflIC&pg=PA381 (in English): "1. Rotastakhm; one having origin of steel; as stout as steel (Avestan scholars are of the opinion that the derivation of the meaning "I am freed" - from Rotastahm - which were supposed to be the words used by Rustam's mother when he was born, is incorrect). 2. Large; very tall; well-built."- see page 456 of "The Cambridge History of Iran (Volume 3)" written by E. Yarshater: https://books.google.nl/books?id=Ko_RafMSGLkC&pg=PA456 (in English): "His name, Rōtastakhm, is Middle Persian (no occurrence of the name has been found in Khotanese Saka, whose literature is chiefly Buddhist and has links rather with India than ancient Iran); even the form used in the Sogdian fragment on Rustam, namely 'rwstmy', appears to be a borrowing from Persian. If Rašdama and Rašdakma in the Elamite tablets from Persepolis should prove to represent the name of the Sistanian hero - a possibility raised by Gershevitch, who suggests their derivation from *rastu-taxma, then Nöldeke's view will have found unexpected support."- https://archive.org/stream/Gershevitch1969AmberAtPersepolis/gershevitch%201969_Amber%20at%20Persepolis%20%20_djvu.txt (in English): "The resemblance to Rustam’s name may be deceptive, but surely justifies an attempt at identification. Supposing the lost syllable to have been tu, one obtains *rastu-taxma- y with the adj. As second component as in *cisd-~vahu- (see Zissawis and cf. GMS p. 252). To the OP noun *rastu ~ < *rastu- (cf. OP (h)ufrasta- scanning — see Noldeke, Nationalepos 12 n. 1). NP Rustam ill agrees with the assumption that the first syllabe ever had a majhiil vowel, but to explain a secondary acquisition of one, Htibschmann’s (« IF », Anz., VIII, 1897, 46) and Noldeke’s (p. 11) view, going back to Justi, JVB, p. VIII, that Rustam’s name was adapted to that of his mother Rodabe, would be sufficient. Sogdian rwstmy was borrowed from Persian, cf, Sogd. Mrtxmy against Pers. Mardum. The earliest datable occurrence of the name so far has been the Armenian Arostom in the fifth century AD."- see note no. 5 on page 2 of "The History of al-Tabari, Volume IV: The Ancient Kingdoms" translated by Moshe Perlmann: https://books.google.nl/books?id=_MtsLf62MwYC&pg=PA2 (in English), which says: "Rustam is derived from Middle Iranian Rōd-stahm. See Markwart, ZDMG, 49 [1895], 642; Christensen, Kayanides, 121ff, 130ff."- https://en.wiktionary.org/wiki/%D8%B1%D8%B3%D8%AA%D9%85 (in English): "From Middle Persian lwtsthm (Rōdstahm)." [noted -ed]