I'm saddened my the fact that a lot of people, especially those who are supposed to be in the know about the Dharmic philosophies make this most fundamental mistake.
As a fellow practitioner of the Dharmic way (an Advaita Vedanta Hindu to be exact) I had to explain the difference many a time, between monism and non-dualism.
The Sanskrit word Advaita is made up of two words, A+ Dwaita
Dwaita = Dual
A = no/negation in Sanskrit
Thus Advaita means "not-dual".
It explicitly refrains from saying its "one", because according to Advaita philosophy, the moment we say "one" we are caught in the trap of dualistic thought, because if there is "one" there is "two"..or more. There cannot be "one" unless there is something that is "not one" to compare it against.
Sadly a lot of neo-Advaitins, along with Buddhists also fall prey to this non-dual= monism equivalency. It could not be further from the truth.
imho Avdaita Hindu Philosphy and What Buddha spoke are one and the same, albeit one talks about the "self" while the other talks about the "not-self" (atman/anatman). however in the non-dual field these two meet...as they are imho speaking about the same thing, but looking at it from different sides.
As atman and anatman are both said to be beyond description, they both transcend the linguistic hurdles associated with them.
Ps: I hope Buddhist members will not mind a Hindu posting here