An ELT Glossary : Correlatives
Correlative expressions consist of two parts. They may belong to various word classes.
Some examples :
Correlative conjunctions - eg either/or, neither/nor, both /and, not only/but also,
if /then etc
She not only got 100% on the test, but also finished in half the time allowed.
If he refuses, then we'll need to change our plans.
Correlative prepositions - eg fromto, between/and
We're open from 9 to 5.
I'm not sure how old he is - but somewhere between 60 and 70, I think
Correlatives may also mix word classes as in the expression as (adv) / as (preposition)
He's as stubborn as a mule.