1 not possible; that cannot occur, exist, or be done (such a thing is impossible; it is impossible to alter them).
2 (loosely) not easy; not convenient; not easily believable.
3 colloq. (of a person or thing) outrageous, intolerable.
Derivatives:
impossibly adv.
Etymology: ME f. OF impossible or L impossibilis (as IN-(1), POSSIBLE)
Useful english dictionary. 2012.