What are the differences between the words Ghaafir, Aghfar, Ghafoor and Ghaffaar?

Each of the four words are nouns derived from the root Ghain-Fa-Ra. The general meaning of the words revolves around the act of forgiving.

Ghaafir: This is an “Active Participle” (Ism-ul-Fa’il) or the doer of a verb. In this case the verb is to forgive so Ghaafir is the one who forgives.

Aghfar:  This noun is an “Elative” (Ism-ul-Tafdeel) and indicates a comparison between multiple active participles – It means more forgiving or most forgiving (Aghfar al Ghaafireen)

Ghafoor: This is the “Resembling Particle” (Sifat-ul-Mushihbah) and refers to an entity who intrinsically possesses the quality of forgiving, as opposed to the active participle which indicates a temporary action of forgiving being performed by the subject. In order to be ghaafir, there needs to be an object (someone who is being forgiven). But one who is Ghafoor, does not require an object and is continuously and permanently forgiving even if there is no one to forgive.    

Ghaffaar: This is the “Intensive Adjective” and indicates the exaggeration or repetition of the base meaning (in this case forgiveness). One can say that Ghaffaar is one who is extremely Ghaafir – one who forgives a lot and again and again. The excess in forgiveness is not in comparison to others. Ghaffaar does not imply a comparison with others (as opposed to Aghfar) and indicates absolute intensity.