1. What do the following words have in common?

HOUR
GRAVITY
TOLERANCE

2. What do the following words have in common?

SALT
STAR
SOLID
MUSIC
BOTTOM
CONCERT
CLIMBING

HINT:
2. The same word can precede each clue.

Answers:

1. They are commonly preceded by ZERO. 
2. Each word can be preceded by ROCK to form a familiar two-word phrase.

Credit #2: GAMES Magazine - July, 2014
Raymond D. Love
A HARD PUZZLE