I have written a sentence using the word adherent. I am not sure if I can write this sentence as I am somewhat confused about the meaning of the word. Please advise.
A large number of adherents waited patiently for the President whom was going to give a speech on his plan to cut taxes by fifteen percent.
Yes, 'adherents' is OK, if you're referring to followers of the President.
But why do you use "whom" when 'the President' is the subject of this clause? Who was giving the speech?
The President was giving the speech.
Compare: A large number of adherents waited patiently for the President whom they intended to present with an award.