The etymology of 助っ人


Recently I came across the word 助っ人, surprised to find out its reading was
"すけっと."

Does its etymology have something to do with 助ける【たすける】 and 人【ひと】? If so, why
the disappearance of た, ひ, and the addition of 促音?




Yes, it is 助【すけ】 + 人【ひと】.

[助【すけ】](https://dictionary.goo.ne.jp/jn/117980/meaning/m0u/) is an obsolete
word that means "help; assistance". The currently used verb 助ける is composed of
た "hand" + すく "assist".

`Noun + 人` was a very productive way to coin a word that roughly means "-er"
or "who is --" throughout older times in Japanese. Many of those words are
still surviving in contracted form today, mostly ending in -うと or -うど, but
very few of them have -っと rendering.

  * 助っ人 < 助 + 人
  * 夫【おっと】 "husband" < 男【を】 + 人 "who is (my) man"
  * 盗人【ぬすっと】 (pre-modern) "thief" < 盗【ぬす】み "steal" + 人

Compare:

  * 弟【おとうと】 "younger brother" < 乙【おと】 "junior" + 人
  * 妹【いもうと】 "younger sister" < 妹【いも】 "intimate woman" + 人
  * 素人【しろうと】 "amateur" < 白【しろ】 "white" + 人
  * 仲人【なこうど】 "matchmaker" < 中【なか】 "middle" + 人
  * 狩人【かりうど】 "hunter" < 狩【か】り "hunt" + 人
  * 若人【わこうど】 (poetic) "the youth" < 若【わか】 "young" + 人

* * *

  * 商人【あきんど】 (old-fashioned) "trader" < 商【あき】 "trade" + 人

**PS**  
Further reading: [人：difference between ひと and
-うと](https://japanese.stackexchange.com/q/14073/7810)

