antipsychotic vs major tranquilliser

antipsychotic and major tranquilliser both are nouns.

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

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

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

antipsychotic (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