Short words:
* A
* AB
* BE
* CAB
* CAR
* CASE
* CRAB
* FAR
* FEAR
* K
* KEAR
* RE
* RECK
* REF
* REK
* S
* SAFE
* SCAR
* SERF
Longer words:
* ABACK
* ABATE
* ABSCESS
* ABSCOND
* BEARS
* CABER
* CAFÉ
* CARES
* CRABS
* FARS
* FEARS
* KAFIR
* REACTS
* REBUFF
* RECAST
* REFERS
* REFRACT
* SCARE
* SCARES
* SCARF
* SCARS
* SEARS
* SERF
Bonus:
* RE- (prefix)
Let me know if you'd like me to try for any more specific words!