sharp
look sharp be quick.
1953Margaret KennedyTroy Chimneys I had … begun an idle flirtation with Maria, … then, perceiving that I should be caught if I did not look sharp, I kept out of her way.
sharp as a needle extremely quick-witted.
☞ A variant is sharp as a tack.
the sharp end
1 the most important or influential part of an activity or process.
2 the side of a system or activity which is the most unpleasant or suffers the chief impact.
3 the bow of a ship.
British humorous