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although, isn't also the entry on JMDict for 威 incomplete? daijisen says: 鎧（よろい）の札（さね）を革や糸で結び合わせること。また、その革や糸。(my translation: the linking together of armor plates using laces or leather straps. Also, that leather strap or lace.) - So I feel you're interpreting the meaning for 白糸威 using the second meaning of 威, while I'm using the first which is more like the method itself, and that brings about slightly different interpretations.
白糸威 meaning says: 鎧（よろい）の威の一。白い糸でおどしたもの。(my translation: one of the methods/ways of linking together armor plates using laces or later straps. Armor plates held together with white laces.) In that translation I've interpreted 威の一 as "one of the methods/ways" because there is also 赤糸威、黒糸威 and so on... I've expanded 威 replacing it with the first meaning of the previous translation, and replaced もの with "armor plates" because the verb おどす is only performed on the さね after all.
I apologize in the case my japanese is not good enough yet and I've misunderstood the whole thing, that's a concrete possibility, but that's the reason I was getting to a slightly different meaning.
I won't advocate on this further, I trust you guys ^_^

I think that might be similar to how suits of clothing can be referred to as "threads" in colloquial English.

The plates are called 札(さね). All of my Japanese and Japanese-to-English dictionaries describe "縅" as the 糸 or 皮 that is used to bind them together.

https://i.imgur.com/RrbFm3R.png

for reference in deciding on the most fitting meaning, this in the link above is the context in which I've encountered the word. It's the description of the 小札(armor plates) and at the bottom of it it says: 用いる紐の色に応じて「白糸威」などの名でよばれる。so I had assumed is referring to the whole concatenation of plates in general using white laces, not only the lace object itself.

It seems this word refers to the laces, not to the plates.
daijr: 鎧の縅の一。白糸で縅したもの。

〈白／しろ／しら／シロ／シラ〉〈糸／いと／イト〉〈威（し）／縅（し）／おどし／オドシ／脅（し）〉

Google N-gram Corpus Counts
╭─ーーーーーーー─┬─────╮
│ 白糸威　　　　 │ 625 │
│ 白糸縅　　　　 │ 279 │ - add (daijirin)
│ しろいとおどし │ 102 │ - add (daijirin)
│ しらいとおどし │   0 │
╰─ーーーーーーー─┴─────╯

I guess [hist] is okay. Maybe [arch].

@@ -6,0 +7,6 @@
+<k_ele>
+<keb>白糸縅</keb>
+</k_ele>
+<r_ele>
+<reb>しろいとおどし</reb>
+</r_ele>
@@ -12 +18,2 @@
-<gloss>plates held together by white laces in a japanese suit of armor</gloss>
+<misc>&hist;</misc>
+<gloss>white laces used to bind plates in a traditional Japanese suit of armor</gloss>