1 point (of needle)

2 sharp

3 shrewd

4 pointed

1 to screech

2 to shriek

1 dagger

1 caustic

2 biting

3 piquant

4 acerbic

5 vitriolic

6 acrimonious

1 best of its kind

2 cream of the crop

1 sharply opposed to each other, with neither prepared to give an inch (idiom)

1 lit. to penetrate into a bull's horn (idiom); fig. to waste time on an insoluble or insignificant problem

2 to bash one's head against a brick wall

3 a wild goose chase

4 a blind alley

5 to split hairs