Gharābah (غرابة) is uncommon, obscure diction whose intended sense is not readily accessible to a competent audience. A word may have a valid Arabic origin and still require unusual research or interpretation in its context.
The introduction cites مُسَرَّجًا from a poetic example to illustrate difficulty in determining the intended meaning.
This does not make every specialist technical term defective. The concern is avoidable obscurity that prevents the intended expression from being readily understood.