1. adjective
a) likely to be affected by or experience something.
Menu listings and prices are subject to change.
b) conditional upon
Hes subject to sneezing fits.
2. noun
a) 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.
“In the sentence ‘The mouse is eaten by the cat in the kitchen.’, ‘The mouse’ is the subject, ‘the cat’ being the agent.”
Her favorite subject is physics.
3. verb
To cause (someone or something) to undergo a particular experience, especially one that is unpleasant or unwanted.
Wikipedia foundation.