Sub
This marine vessel sinks below the surface.
Submarine
To send a signal across a distance
Transmit
Clothing worn below
Undergarment
Not normal
irregular
Middle of the season
Midseason
Below freezing temperature
Subfreezing
To write or say in a different language
Translate
To draw a line under something
Underline
Can not be removed
Irremovable
To count wrong
Miscount
A train that travels below the ground
Subway
To see through
Transparent
To not be at the proper temperature for food
Undercooked
Can not be resisted
To put together wrong
Mismatch
Below your level of thinking
Subconscience
Going across the continent
Transcontinental
To be below the arm
Underarm
Not responsible
Irresponsible
Middle of the Week
Midweek
A topic that is less important than main topic
Subtopic
To change into written form
Transcribe
To be below the ground
Underground
Can not be rationed with
Irrational
Not use correctly
Misuse