The engine suddenly 'roared (back) to life'. [=it made the loud sound of an engine and began running well]
The audience 'roared' with laughter. [=the audience laughed loudly for a long time]
The fans were 'roaring' [=yelling and cheering loudly] after their team scored.
(..) Good night, sweetheart. ANIMATRONIC BO Y: Night, Mom. Kitty! No, Boo, no, no! Now, give us a big, loud roar. Mr Waternoose, there's no time for this. Come on. What are you waiting for? Roar! But-but-but, sir! Roar! ( groans ) ( roaring ferociously ) ( shrieking in terror ) ( gasps ) ( roaring ferociously ) (..)2001 Monsters, Inc.