@realsimon

something is COMMON/SAME for friends? Yes. Here what is ARKA of arkaDAŞ? Meaning of ARKA is BACK or BACKSIDE. Why we take backsides of friends are same/common? Because you rely on your backside, backdide is OK and trustable...

In all languages and cultures trustibility is important I guess. Now we can bring FRIEND and FAMILY together...

@realsimon

or more than 2 person.

- For example physicists are occupationTAŞ or professionTAŞ, here occupation/profession is COMMON or SAME for them.
- For example Germans are homelandTAŞ, here homeland/Germany is COMMON/SAME for Germans.
- For example abdomen (= karın in Turkish) part of mother is COMMON/SAME for brothers, because of this Turkish of BROTHER is karınDAŞ. In time this karınDAŞ had turned to karDEŞ.

Now lets come to FRIEND, Turkish of FRIEND is arkaDAŞ. Does it seem ++×

@realsimon
Origin of the proverb and origin of a word are not same. Origin of a proverb can be found in understandings of cultures I guess. Lets see one from Turks ;

It will not be about the etymology of FRIEND but the proverb. From proverb we may understand the approach under FRIEND.

I will give an example from another language (Turkish) to learn how the person/individual and the folk/society think.

In Turkish there is a suffix (TAŞ or sometimes DAŞ) adds meaning of COMMON or SAME for 2 +

@alex

-) In Türkiye alphabet ш = ş
-) In many Kazak Turkish words we see s instead of ş.
Taş (Tr) = Stone (Eng) = Tas/Tac (Kz)
Kış (Tr) = Winter (Eng) = Kıs/кыс (Kz)

What I mean is that you can check бошка in Kazak as бас too.

-) Some examples from Türkiye Turkish including 'baş' having meaning HEAD are ;
Başkan - President, head
Başbakan - Prime minister
Başlık - Hat
Başlık - Title

having meaning MAIN≈FIRST are ;
Başlamak - to start
Başrol - Lead role