What do the following words have in common?

1. LOG
2. COMB
3. TONIC
4. PILLAR
5. LIST
6. GORY

HINTS:
All the words can be preceded phonetically by the same four letters. There are spelling changes in #4-6. 

Answers:

Each word can be preceded phonetically by the letters CATA:

1. CATALOG
2. CATACOMB
3. CATATONIC
4. CATERPILLAR
5. CATALYST
6. CATEGORY