Whats in a word...? Kastane ~Katana
Whilst the Edo period in Japan heralded some interesting political visits to Sri Lanka it is with a broad brush that I apply some potential to this word puzzle... and I suspect that like other similar puzzles like Kattara, Qudderah, Katta etc etc this one may rest forever surrounded in the usual mists of time ..
Quote" Etymology and loanwords. "Katana" is the term now used to describe nihontō that are 2 shaku (606 mm / 23.9 in) and longer, also known as "dai" or "daito" among Western sword enthusiasts although daito is a generic name for any long sword.
Pronounced [katana], the kun'yomi (Japanese reading) of the kanji 刀, originally meaning dao (sword) or knife/saber in Chinese, the word has been adopted as a loanword by the Portuguese language. In Portuguese the designation (spelled catana) means "large knife" or machete.
As Japanese does not have separate plural and singular forms, both "katanas" and "katana" are considered acceptable forms in English".Unquote.
Whilst there are some links in the Buddhist nature Bothavista and a few similar letters in each alphabet Sri Lankan / Japanese and a similar word order... it is far from clear if there was any involvement in a word link though one website actually plainly points to the word Kastana as having evolved from the Japanese word Katana but without proof. see http://karava.org/other/mudaliyars
at para 3 under Mudalyars...I therefor have the Japanese obtained Portuguese word as purely co-incidental.