1. What do the following words have in common?

FIG
MAIN
MUST
HIND
SLOW
SMUG
MAIL

2. What do the following words have in common?

ORE
VICE
JUST
HERE
MIRE

HINTS:
1. Changing one letter in each word will create six new, related words.
2. The same two letters, placed in the same position, will create new words.

Answers:

1)
FOG
RAIN
MIST
WIND
SNOW
SMOG
HAIL 

2. Each word can be preceded by AD:

ADORE / ADVICE / ADJUST / ADHERE / ADMIRE