The words and phrases in the two sets below have in something in common. Can you determine what it is?

 Set I
1. GONE ASTRAY
2. LOW ESTIMATE
3. MINOR THEME
4. MEN'S OUTHOUSE

Set II 
1. WORKOUT ROUTINE
2. MOLLYCODDLE
3. SUPERCHARGED
4. CAUGHT UNAWARES
5. LAB ASSISTANT
6. CARPATHIAN MOUNTAINS

Answers:

Both sets of words and phrases conceal hidden, related words:

Set I:
1. gonE ASTray
2. loW ESTimate
3. miNOR THeme 
4. men'S OUTHouse

Set II:
1. workouT ROUTine
2. mollyCODdle 
3. suPERCHarged
4. caughT UNAwares
5. laB ASSistant
6. CARPathian mountains