essentially

basically, fundamentally, radically, at bottom, at heart, centrally, originally, intimately, chiefly, indispensably, naturally, inherently, permanently, determinately, necessarily, primarily, significantly, importantly, at the heart of, in effect, in essence, au fond (French), in the main, all the more, characteristically, intrinsically, substantially, typically, vitally, approximately, quite, actually, truly, really, factually, materially, virtually, more or less so; see also principally.

Antonyms apparently*, superficially*, on the surface.