The other word I’d like to talk about is 入る(hairu), “enter.” There’s also the word iru, “enter”, which has got the same spelling. iru in that meaning is the archaic version of hairu and to be found in set expressions and literary texts.

Anyway, the origin of hairu is quite interesting, at first glance it might look as if it had nothing to do with iru. But in fact, it is a contration of haiiru, which, when written with kanji, reveals its origin: 這い入る=”crawl”+”go in.”

To make this entry a bit longer and to train reading Japanese dictionaries, let’s take a look at the 精選版日本国語大辞典. Feel free to ignore the italic part, I just added it because the actual explanation refers to it. The “*” sign marks an example.

はい・る (はひる)【入・這入】
(1) 名詞形「はひいり」「はいり」は中古から例があり、動詞「はひいる」から生じたと考えられる。
(2) 動詞「はいる」の初期の例は「這う」の意が強く、①の挙例「平家」も、覚一本では「はいり」であるが、百二十句本では「這(ハイ)入て」とあり、「這う」の意が薄れた後でも①㋺の「幼稚子敵討」にも「這入る」の表記が用いられている。
(3) 自動詞「はいる」に対する他動詞形は下二段動詞「いる(いれる)」である。

So we find evidence that at first the hau(crawl) element had been dominant in hairu, and that over time this meaning slowly began to fade out, leaving us solely the meaning “enter” today.

PS: How did you manage with the dictionary entry? On a side note,