As nouns the difference between vassals and subject
is that
vassals is while
subject is (
label) in a clause: the word or word group (usually a noun phrase) that is dealt with in active clauses with verbs denoting an action, the
subject and the actor are usually the same.
As an adjective subject is
likely to be affected by or to experience something.
As a verb subject is
to cause (someone or something) to undergo a particular experience, especially one that is unpleasant or unwanted.