1. What do the following words have in common?

LIP
SAP
GEL

2. What do the following words have in common?

ORE
JUST
VERB
EQUATE
DICTION

HINTS:
1 and 2: It involves added letters.

Answers:

1. The letters ID can be added at the end of each word to make a new one:

LIPID
SAPID
GELID

2. The letters AD can precede each word to make a new one:

ADORE
ADJUST
ADVERB
ADEQUATE
ADDICTION