Planes instead of Densities

[Manjushri]

My understanding is that they are synonymous.

16.50 Questioner: Thank you. Is it possible for you to give a small description of the conditions [in] fourth density?

Ra: I am Ra. We ask you to consider as we speak that there are no words for positively describing fourth density. We can only explain what is not and approximate what is. Beyond fourth density our ability grows more limited still until we become without words.

That which fourth density is not: it is not of words, unless chosen. It is not of heavy chemical vehicles for body complex activities. It is not of disharmony within self. It is not of disharmony within peoples. It is not within limits of possibility to cause disharmony in any way.

Approximations of positive statements: it is a plane of a type of bipedal vehicle which is much denser and more full of life; it is a plane wherein one is aware of the thoughts of other-selves; it is a plane where one is aware of the vibrations of other-selves; it is a plane of compassion and understanding of the sorrows of third density; it is a plane striving towards wisdom or light; it is a plane wherein individual differences are pronounced although automatically harmonized by group consensus.

Also, if you read 47.8 it may become more clear to you that
Astral (emotional) = 4th Density
Mental (deva) = 5th
Etheric = 6th
Buddha/Soul = 7th