infliction vs pain in the ass

infliction and pain in the ass both are nouns.

Word	Noun	Adjective	Verb	Adverb
infliction	Yes	No	No	No
pain in the ass	Yes	No	No	No

As nouns, infliction and pain in the ass are synonyms defined as:

infliction and pain in the ass: something or someone that causes trouble; a source of unhappiness

Other synonyms of infliction include annoyance, bother, botheration, nuisance, pain, pain in the neck.

infliction (noun)	pain in the ass (noun)
the act of imposing something (as a tax or an embargo)	something or someone that causes trouble; a source of unhappiness
an act causing pain or damage
something or someone that causes trouble; a source of unhappiness