Considerably
Fairly, Quite
adverb, な adjective
It's possible that it's considerably considerable. It's considerably, fairly, and quite... something. Also please note that this is almost always written in kana and not kanji. But, we're learning kanji here, so gosh darn it we're going to learn some kanji.
The reading is the same as the reading you learned with the kanji.
日本で初恋の人にバッタリ出くわした時は、可也驚きました。
I was quite surprised when I bumped into my first love in Japan.