Fore -
The part of the arm between the elbow and wrist.
Forearm
A smaller set made from a larger set.
Subset
Beneath the surface
Underground
Overboard
To heat before using
Preheat
To state expected future occurences.
Forecast
A ship designed to go under water.
Submarine
To mark under the line
Underline
To feel great joy
Overjoy
A time before recorded history
Prehistoric
The fathers that came before you.
Forefathers
An underground electric railway.
Subway
Beneath the water
Underwater
To hear something you weren't supposed to hear
Overhear/d
To pay in advance
Prepay
A person in charge of a group of workers.
Foreman
To sublease.
Sublet
Not of the right age
Staying for one night
Overnight
The time before a child is old enough to be in kindergarten.
Preschool
A short introduction of a book.
Foreword
A secondary title
Subtitle
Something worn under pants
Underpants
Late or past due
Overdue
An affix placed before a word stem
Prefix