nitty-gritty vs mental object

nitty-gritty and mental object both are nouns.

Word	Noun	Adjective	Verb	Adverb
nitty-gritty	Yes	No	No	No
mental object	Yes	No	No	No

As nouns, mental object is a hypernym of nitty-gritty; that is, mental object is a word with a broader meaning than nitty-gritty:

nitty-gritty: the choicest or most essential or most vital part of some idea or experience
mental object: the sum or range of what has been perceived, discovered, or learned

Other hypernyms of nitty-gritty include cognitive content, content.

nitty-gritty (noun)	mental object (noun)
the choicest or most essential or most vital part of some idea or experience	the sum or range of what has been perceived, discovered, or learned