[A. G. Maisey]

Yes, as with many things of foriegn origin in Jawa, the original music played by Portugese speaking people there has probably morphed into something more uniquely Javanese in its nature. As has the instrument which gives it its name; the cavaquinho is like a four stringed uke, but the kroncong (instrument) used in kroncong is most often a three stringed instrument, although it can sometimes be four strings, and has a couple of different tunings. They don`t even call it a kroncong these days, it gets called "cuk" and "cak", depending on pitch.
Kroncong is credited with contributing to langgam jawa too, as well as campur sari, and even dangdut, but I think dangdut owes more to the "pop melayu" of thirty or so years ago.

Anyway, regarding the existence of the word "sangkur" prior to existence of bayonets. I`ve looked at the instances given, and checked a couple of references, and my comments follow.


Sangkur Temple in Bali

It seems there are at least a couple of temples in Bali that incorporate the word "sangkur" in their names. There is Pura Pucak Sangkur on Bukit Sangkur (AKA Bukit Resi), there is Pura Hyang Sangkur. There could well be others.

I do not know the meaning of "sangkur" in this context, and have been unable to find out.

Dictionary checks tell me that in Balinese there are two meanings to the word "sangkur", neither of which seems to be appropriate to the name of a temple:-

sangkur:- variation of "sangkut":- to hook onto (Anandakusuma)

sangkur---without a tail (Sutjaja)

then there is the word:- sangku---holy water container (Sutjaja)

which is a root word coming from Old Javanese and Kawi, but this is probably also not suitable, because of the use of "hyang" in one of the pura names; "hyang" is a title for a diety.

It would seem that in Balinese the word "sangkur" has a meaning associated with the Bali-Hindu faith.

This being so, I think we can probably discount the occurrence of the word "sangkur" in Bali, as a possible contributor to its use as meaning bayonet in Indonesian.

Sangkur Mountain in Sunda

I do not have access to a Sundanese dictionary, so have been unable to find the meaning(s) for "sangkur" in Sundanese. However, there is a Sundanese song:- "Sangkur Ratu", which is consistently translated to English as "The King`s Sword". Possibly in Sundanese "sangkur" has the meaning of "sword", which is similar to, but is not, a bayonet.

The City of Banjar has an official history that only begins in 1937. I do not know how long Banjar existed as a small town or village prior to becoming sufficiently important to have its own lambang (logo, coat of arms), but this lambang was designed after Indonesian independence, as the star used in the lambang was drawn from the Pancasila.

Similarly I do not know how long Gunung Sangkur has been known as this.

I do not think that we can presume that Gunung Sangkur was known as Gunung Sangkur since ancient times, and at the present time the meaning of "sangkur" in Sundanese is still not very clear.

Accordingly, I believe we can dismiss the possibility that the occurrence of the word "sangkur" in the Sundanese language has contributed to the use of "sangkur" as the word for "bayonet" in the Indonesian language.

Sangkuriang

The proper name "Sangkuriang" could be a combination of "sangkur"+"iang", but I believe it is more likely to be a combination of "sangku" and "riang", if it is a combination at all."Sangkur" is Indonesian (Bahasa Indonesia), which has only been in general use since after independence in 1946, and perhaps means "sword" in Sundanese, but "iang" would seem to me to not have any meaning. "Sangku" is an older word that occurs in other languages, and "riang" has the meaning of "glad, joyful", but I do not know where this word originates. We really need a Sundanese dictionary, and probably an Old Sundanese dictionary too.

Further Findings

However, I have found that in Sanscrit (Macdonell) the word "sank-u" exists, where it has the meanings of :- "nail, spike, arrow, peg, spear, dart, stake".

In Old Javanese (Zoetmulder) the word "sanku" has several meanings:
bowl, nail, arrow, spear, gnomon,+ a specific type of unknown weapon, possibly a spear+ a specific fixed time.

The meanings relevent to this discussion would be :- arrow & spear, as well as the unknown weapon.

In Modern Javanese the word "sangku" also has several meanings:-
"water bowl, basin" (Robson & Wibisono)

"arrow" (Prawiroatmodjo, Balai Bahasa Yogyakarta)

" metal bowl, tub, copper bowl" (Prawiroatmodjo)
" metal bowl" (Balai Bahasa Yogyakarta)

We already know that in Modern Javanese the word "sangkuh" means "bayonet".

Conclusion

Bearing in mind the way in which a bayonet is used, that is as a fixture to the front of a weapon (firearm) that hurls projectiles , and accordingly could be seen as either an arrow (Old Javanese:- "sangku"), or in its fixed form, as a spear (Old Javanese:- "sangku"), I think that at this point we may reasonably be able to state with some degree of certainty that the Modern Javanese word "sangkuh", meaning "bayonet", comes from the Old Javanese word "sangku", meaning "arrow", and "spear", and that this Old Javanese word "sangku" comes from the Sanscrit "sank-u" meaning, amongst other things, "arrow", and "spear". The Indonesian word "sangkur" probably comes from the Javanese word "sangkuh".

Apologies

I admit that it would have saved a lot of time and a lot of trouble if I had done this work in the first place, instead of throwing wild ideas around, but this sort of thing takes time, in this case about two hours, and time does have a value. I probably should not have commented on this sangkuh in the first place. All my comments ultimately did were to cause work for other people, for which I apologise, and for myself.