Definitions for main clause
Random House Webster's College Dictionary
a clause that can stand alone as a sentence, containing a subject and a predicate with a finite verb, as I was there in the sentence I was there when he arrived.
Ref: Compare subordinate clause.
main clause, independent clause(noun)
a clause in a complex sentence that can stand alone as a complete sentence
A clause that can stand alone syntactically as a complete sentence; contains at least a subject and a verb.