pain in the ass vs infliction

pain in the ass and infliction both are nouns.

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

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

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

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

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