This question already has an answer here:
I've noticed a couple of words with the character 八 that have (seemingly) nothing to do with the number 8.
- 八百屋【やおや】 - greengrocer
- 八つ【やつ】当たり【あたり】 - taking out anger on someone
- 八丁【はっちょう】 - skillfullness
Furthermore, this is the only number which I've noticed this pattern on. All other words consisting a number have a much more obvious relation, (even when it's a 一).
On jisho.org, the count of #words containing each of the numeral characters shows a noticeable spike on 八 as well.
一 二 三 四 五 六 七 八 九 十 1713 787 1264 438 364 196 172 357 308 320
And here's a table of how common each is in newspapers. Doesn't really show anything but I thought to include it since I looked into it as well. I wonder what the count would be if 九州【きゅうしゅう】 was stripped from the count on 九.
一 二 三 四 五 六 七 八 九 十 2 9 14 47 31 93 115 92 55 8