What's the difference between i.e. and e.g.?
A form of rock-and-roll music with a simple, driving beat, usually played on heavily amplified guitars (1960s+ Rock and roll)
Severe; dour and pugnacious; tough: the old hard-rock guy who would line up all the cocaine users and shoot them
[1923+; probably fr the difficulty of hard-rock mining as distinct fr other kinds; influenced by rock-hard]