Definition of "Idist"

[…] but on the other hand the Idists are not so few as their adversaries generally say, and among them are a good many who before 1907 were leaders and editors of Esperanto in the various countries.

2010, Otto Jespersen, “History of our Language”, in Selected Writings of Otto Jespersen (Routledge Revivals)‎, Routledge