ipsum, adv?

[Lavrentivs]

qualitates igitur appellavi quas ποιότητας Graeci vocant, quod ipsum apud Graecos non est vulgi verbum sed philosophorum,
(Cic., Ac. I.25)

is ipsum here adverbial? (can n. acc. generally be adv?)

[ptolemyauletes]

I think it's just acting like an intensifier. 'Which among the Greeks is itself (in and of itself) not a word of the common people but of philosophers.'

[gerases]

ipsum here is an adjective modifying "quod" and "verbum", i.e., "quod ipsum verbum", "which word itself".

is ipsum here adverbial? (can n. acc. generally be adv?)

Some neutral adjectives have become adverbs. E.g.: facile, multum, paulum. See Bennett 77.3.