antipsychotic agent vs major tranquilliser

antipsychotic agent and major tranquilliser both are nouns.

Word	Noun	Adjective	Verb	Adverb
antipsychotic agent	Yes	No	No	No
major tranquilliser	Yes	No	No	No

As nouns, antipsychotic agent and major tranquilliser are synonyms defined as:

antipsychotic agent and major tranquilliser: tranquilizer used to treat psychotic conditions when a calming effect is desired

antipsychotic agent (noun)	major tranquilliser (noun)
tranquilizer used to treat psychotic conditions when a calming effect is desired	tranquilizer used to treat psychotic conditions when a calming effect is desired