In Germanic the dual is lost but traces can be seen in the rare "R" plural

doubling has special orthographic provenance:

𓏏𓏏 Teti ≈ Tyréis

𓈋 2 double < dabr ⋍ደብር ⋍ ⲧⲱⲩ tvr 𒋛𒀀 diri 𓈋 > tell 𓏏𓏏 󴄬

𓈋 du₆ᵃˡ 𒇯 tell

2 dvał 𓈋 dual duo dos 2 多 🌙 dale ᎣᏓᎸᎢ odalvi dził Tal دره dareh valley
dual 𓏏𓏏 Teil 𓄜 𓄛 < tear track drag
dual vs duan 𓌢 𓈖 𓏌 𓏲 𓀀 𓀀 counterpart contestants companion ⇔ twin 𓌢 2 dual ↔

𓈋 ≈ 𒆴 ⲧⲟⲟⲩ toou® тау طُور ṭūr טוּרָא ṭūrā սար tour ተራራ tärara ⴰⴷⵔⴰⵔ 𓈉 𓇾 "mountain" tower land

د و ل d-ov-ł dual:alternate دَالَ dāla:rotate ⇔ track د و ر d-ov-r √tour circle

𓈋 dule = sky @ Fula

𓈋 дубура dubura Berg

𒌇𒆕 DU 2 𓏙𓇮𓏚 DURA 3

𒁲 DI 𒉌 DIG

A grammatical form between singular and plural,
the dual is preseved in some european languages.
In Egyptian it is written as 𓏮 𓏭 𓇌 𓇋𓇋, read as ee,ei,ii,j
In Proto-Indo-European it has forms of -h₁e -ih₁ -oyh₁
In Arabic, bahrayn is the dual form of bahr ("sea") Bach⇨Bahrain⇨Bäche Baqua Bug
The late reading of 𓏭 𓇌 𓇋𓇋 as ay is consistent with the Arabic bahrayn

There is a tendency for the loss of the dual as a productive form in later Egyptian.

Provocative reading: suffix 𓏮 as di ti or bi 𓏭 𓇌 𓇋𓇋

𓃀 Ein Bein (1 foot 1 podOn 1 podUs) on/as/us=1 eins
𓂾𓃀 Beide Beine (2 poDi/feet) di=2

N:R

A lost dual form is related to the old plural suffix
二 èr -er Haus => Häuser child=>children
二 ni -en Straße => Strassen

𒉣𒉪 nun => nir
𒁴𒁴 dim² Türme tower
𒍘𒍘 du₉ دریغ dariğ Trauer #2*dun bědování دژوان dožvân
𓁹𓁹 ⲓⲣⲓ,ⲓⲉⲣ eyer 2 Eier eye(s)
𓃀𓃀 पैर pair پیر perna Latin 󳠖 punro pa по পা pierna ⇔ 발 bal parsa 𓄙 Ferse √part πόρ pór

𒉣 nun => 𒉪 nir

𒉆𒉣 nam-nun ˢʸnamnun magnificence magnificence
𒉆𒉪 nam-nir ˢʸnamnir supremacy supremacy

All plural / dual forms -r -n -ti are present in Egyptian and confused:

𓁹 eye ⲓⲣⲓ,ⲓⲉⲣ 1. eyer erst / 2 Eier
𓁹 𓏏 𓏮 eyes ⲓⲁⲧ⳼ eyeth ido@Hausa
𓂝 𓈖 𓁹 eye Auᵍen ein 1 eyen ዐይን ʿäyn yǎn 眼 𒅆 IGI / īnu 𒌋𒈨 10100=1000(𓆼)

All plural forms have singular variants:
bir iri (1 eye)
ein eyen ዐይን ʿäyn (1 eye)
first? ⲓⲁⲧ⳼ (1. eye)

bi/du/tu 𓏏𓏏 as syllable for duality already was present in Egypt:

1 𓌠𓏤 bone (Har)poon𓌡 vs 𓌟𓏤 boin (binary) 𓃀𓃀 𓄹𓄻vs
2 𓌟 thun,toe ⋍ keras 𓈎𓋴𓌟 (horn)
2 𓈇 tawi two-towns | two-lands dawlant(AR)=state vs län.der𓇾
2 toe 𓃅 endow(dotier) deva 𓃅 devine 𓊹𓊹@Hindi vs 𓃃 𓊹𓊹𓊹 nTr
2 dvał 𓈋 dual duo dos 2 tal dale! valley
2 d*,tu,tha 𓂋𓌟 rid reed ritual kathar vs ivory 𓍋𓃀𓅱𓌟 ai.b.u.ry[d]
2 tion 𓎼𓈖𓏌𓅱𓏏𓌟𓌟𓌟𓏛𓏛𓏛 generations*
2 tyà 亚 丫yā:fork 亞 tyre asia
2 𓌢 down duan
2 𓏮 du [𓊃𓈙𓏮𓅹 gynishdu/zhnízdo=nest]
2 𓏮 two 𓏌𓏮 #Number
2 T+𓏮=TWO 𐠰𓏮=𐠱=TU@Cypriot
2 𓌢 ꜩwin T22 twin, zwein cin@coptic kin gyn snw/ßwn@EGY𐠮𐠯 @Cypr çun@Albany
2 ta’owm=twin@SEM
2 𓌢𓏌𓏮 cwn ⇔ gon kin cen: incense = 𓊹An.𓌢ꜩ.𓈖n.𓍿c.𓂋r𓆴𓈒𓏥 𓍑𓊮
2 toon 𓍃 don't ⇦ SchlitTen
2 Shatwom 𓈙𓍃 שְׁתַּיִם sTwomn 𐎘𐎐𐎎 𓍏?
2 duo 多 duō
2 tu 𓇑𓇑 Nature = 𓈖𓇑𓇑𓏏𓇳 nattura (𐦌NE 𓇑𓇑tu 𓇓shu 出chū 屮chè 子zi )
see numbers, cosmos
2 tit 𓏏 dad=breast

Super roots:
𓃀𓃀 BEIDE BOTH PODES/PODEN ⇔ apart, but
𓏏𓏏|B'D'T| dual dough/teig D/Telle breδt breast/tit𓏏𓏏
bone 𓌠𓏤 vs 𓌟𓏤 Nepthune?

Contrast with Plural -n -en -men vs dual -mwn -𓅱
2 Snwi 𓈙𓈖𓅱𓇋 - zwei 水 shuǐ šina@Akkat eth’nen@Arab
2 min 𓏠𓈖𓅱 𒋰 𒈫 MIN 门 門 mén vs many 𓏠 smni cmwin twin ?
2 min 𓏠𓈖𓅱 𒋰 𒈫 MIN 门 門 mén vs many 𓏠 𓅱 -mun -mwn -wn -w
In Arabic, bahrayn is the dual form of bahr ("sea")

𒂃 DUḪ TUḪ (tit𓏏𓏏 ⇔ Brust 𓇣?)

𓁹𓁹 eyer ⲓⲉⲣ eyeth ⲓⲁⲧ⳼ ido@Hausa eye.duo

2 both pair binary :
𓃀 𓈖 𓏏 𓏮 𓂒 𓂒 | pair of breasts, nipples | bin*2 tittis = 𓏏𓏏𓏮𓂒 ☑
𓃀 𓈖 𓏏 𓏮 | two baboons (which greet the morning sun) | Viannas ⇔ Venus! [[

𓉿 ⋍ 𓈐 track *dorga доро́га doróha drome 道路 どうろ dōro 도로 doro road reversed
𓉻 𓂝 𓈐 | dort | here, there, yonder | 𓉻 dart
𓉻 𓂝 𓉿 | door | 鬥門 dòumen dual

𓈋 𓃒 in
NL7 𓈦 nome six, Khaset, capitals Khasu ⲥϦⲱⲟⲩ 𓆼𓋴𓅱𓅱𓏏𓊖 #ḫꜣswwt (Xois) Ξόης Ξόις سخا Sakha •ksont Buto 𓃒

𒅆𒅆 bad₅ ≈ beat in 𒅆𒅆𒅆𒅆 bad₅bad₅ “defeat” #dabdû •beat (in battle) dual duplication

𒂉 dur 𓈋 σφῦρα sphûra Spur, Rain (Feldrand) ridge ⇔ die Rampe ≈ rump :

𒂉 dur 𓈋 دُبْر dubr buttocks =>

𓈋 double ᵈheap 𒅖𒁾𒁀 sahar-dub-ba saharduba rubbish heap 𒄸 HUB₂ heap

鬥 dou double-door-wing 𓉿 door-leaf 󲁄 󲁆 janah جناح 󲁅 󲁇 𓆓 𓈖 𓎛 𓆃 (door) wing 𓂧 𓈖 𓎛 𓆃 ⲧⲉⲛϩ tᵊnh ডানা ḍana :