[mariusgmioc]

Regarding the term "bichak," to me it is quite clearly a direct phonetic transliteration of the Turkish word "biçak" simply because English doesn't have the letter "ç" and neither do most of keyboards. It is exacltly the same way as the Turkish word "kiliç" is spelled in English as "kilij" using a spelling that is closer to the way the word should be read. All the other forms, might simply be alternate, sometimes misspelled phonetic transliterations.
As with respect to the meaning of the word, yes in Turkish it means simply "knife" but at the same time it has become a associated with a specific Ottoman type of knife, the very same way the Persian word "kard" which also means "knife" has become associated with the well known specific type of knife that originated in Persia.
PS: The word "kiliç" means "sword" in Turkish, but it has become associated with the specific Turkish saber.