This is a term which afaik was created when I was trying to learn Turkish. Here is again a false friend warning for you: arka is NOT friendly but ‘as a friend’, ‘related to a friend or friendship’. Arka’tan means friendship. ‘arka means ‘to be friend [of]‘. It can be used transitively or intransitively.
Example: Syku ji Tamakil min’arka. (Syku and Tamakil 3PL-be.friends: Syku and Tamakil are friends.)
BTW: Random stuff people used as search term to find this piece of the internet in this week: conlang blogs, metaphorical sense of the word, handwriting text, easy conlang (thanks google for calling my language easy), do you like relexes conlangs (WTF‽), what to do first in a conlang? (seriously‽) and “most complete” conlangs (there is no thing like that until we have a measurement of completeness. Seriously, what are you smoking‽ And where can I get some of it‽).