complex (not simple or straightforward)

easy / simple, uncomplicated / brief, light, short

ease / simplicity / lightness, brevity

(chiefly in mathematics, physics) for simplicity; for the sake of simplicity

extraordinary, unusual

emergency

very; extremely / exceedingly; tremendously

solution, settlement / (music) Progression from dissonance to consonance; a chord to which such progression is made; resolution

(transitive) solve, resolve, settle (a problem, a trouble, a criminal case) / (intransitive) be solved, be settled / (intransitive) can be solved; be soluble

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter