Synonyms for " subject"

In fact, the simplest sentence does not even require an object, just a subject and a verb.

I am writing. (subject = I; verb = am writing)

I am writing a message. (subject = I; verb = am writing; object = a message)

A simple sentence consists of a subject, a verb and an object.

For example:  Raju plays hockey.

Raju is a subject of a sentence.

Play(s) is a singular verb.

hockey is an object of a sentence.

I hope this helps.