nucleolar organizer vs nucleolar organiser

nucleolar organizer and nucleolar organiser both are nouns.

Word	Noun	Adjective	Verb	Adverb
nucleolar organizer	Yes	No	No	No
nucleolar organiser	Yes	No	No	No

As nouns, nucleolar organizer and nucleolar organiser are synonyms defined as:

nucleolar organizer and nucleolar organiser: the particular part of a chromosome that is associated with a nucleolus after nuclear division

Other synonyms of nucleolar organizer include nucleolus organiser, nucleolus organizer.

nucleolar organizer (noun)	nucleolar organiser (noun)
the particular part of a chromosome that is associated with a nucleolus after nuclear division	the particular part of a chromosome that is associated with a nucleolus after nuclear division