We found one dictionary that defines the word to which:

Phrases: the extent to which, the degree to which, number to which another is added, the extent to which something is fake, relating to that which is telling, more... ▸ Words similar to to which ▸ Usage examples for to which ▸ Idioms related to to which ▸ Wikipedia articles (New!) ▸ Words that often appear near to which ▸ Rhymes of to which ▸ Invented words related to to which