adverb
Colloquial adverb expressing a moderate degree; similar to わりと but slightly more casual. Often used when something is more than expected but not extremely so.
See also: 割り方
この店のラーメン、わりかし美味しいね。
This shop's ramen is quite good, isn't it?
今日はわりかし早く帰れた。
I was able to go home relatively early today.
Derived from 割り (わり, 'proportion') + かし (emphatic particle). The exact historical development is uncertain, but it functions as a colloquial adverb of degree.