つうと言えばかあ（読み）ツウトイエバカア
デジタル大辞泉の解説
《「つうと言えばかあと答える」から》互いに気心が通じ合って、
ちょっと言っただけで相手の言おうとしていることがわかること。
「つうと言えばかあの仲」→つうかあ
https://www.etymonline.com/search?q=between
between (prep., adv.)
Old English betweonum, Mercian betwinum, "in the space which
separates, midway, in the midst, among; by turns," from bi- "by"
(see by) + tweonum dative plural of *tweon "two each"
(compare Gothic tweih-nai "two each;" from PIE root *dwo- "two").