'Fladry' is a comparatively recent adoption in English from Polish, with a putative origin in German. The Double-Tongued Dictionary gives this definition and partial etymology:
fladry n.pl. a string of flags used to contain or exclude wild animals. ... Etymological Note: According to Polish Scientific Publishers (Wydawnictwo Naukowe PWN, SA), fladry is the plural of flader, which comes from German. It is not specified which German word, but it’s probably related to flattern ‘to flutter.’ It is probably not related to the Polish flÄ…dry, the plural of flÄ…dra, which according to the Oxford PWN Polish English Dictionary (2002, Oxford University Press) means “1. flounder, flatfish; 2. slattern, slut.”
I have found 'fladry' in English in the sense of "a string of flags etc." as early as 1993, in a technical paper titled "Status and Management of the Wolf in Poland" (Biological Conservation; see, for example, the abstract).
Alongside the current efforts to manage wolf packs after their reintroduction to areas of the US where they may prey on domestic animals, 'fladry' has been adopted into the commonplace English lexicon, although it does not yet appear in OED or other well-established print and online dictionaries.
The question is
- What is the German etymon of Polish fladry, from which last the English word derives?
I am hoping for an authoritative answer based on at least one quotable source.
My guess is that the German etymon is, in fact, flader, a German word meaning "streak, vein". In the form 'flaser', which derives from a dialect version of German flader, the word finds current technical use in English to denote a structural characteristic of sedimentary rock:
(Image from Geologic Digressions, copyright Brian Ricketts, at https://www.geological-digressions.com/tag/flaser-bedding/.)
Although the rock structure and a line of flags in fencing do not, at first blush, seem to resemble each other much, part of a diagram in a 1968 paper, "Classification and Origin of Flaser and Lenticular Bedding" (Sedimentology, Volume 11 (1‐2) – Oct 1, 1968), which attempts to more precisely define and subdivide sedimentary bedding types, appears to make a more graphic connection:
Further research turned up flader in a 1912 English-Polish dictionary, where it is defined as "streak in wood". Because Polish Scientific Pub. state that fladry is the plural of flader "which comes from German", and given that flader is defined in A German-English dictionary for chemists as "curl, speckle, streak", my guess seems somewhat supported by that evidence.