What do the following words have in common?

1)
PAR
MOM
STUD
STRING

2)
BID
GET
EGO
AGE

Answers:

1. Each word can be followed by ENT to make a new word:

PARENT
MOMENT
STUDENT
STRINGENT

2. Each word can be preceded by FOR:

FORBID
FORGET
FOREGO
FORAGE