WordNet sense 1 ((used of eyes) open and fixed as if in fear or wonder):

agaze

WordNet sense 2 (used of mouth or eyes):

open, opened

WordNet sense 3 (without qualification; used informally as (often pejorative) intensifiers):

arrant, complete, consummate, everlasting, gross, perfect, pure, stark, thoroughgoing, unadulterated, utter, double-dyed, sodding, consummate, perfect

WordNet sense 4 (not diminished or moderated in intensity or severity; sometimes used as an intensifier):

unmitigated

WordNet sense 5 (with a stare):

staringly