Two Letters:
* ab
* ac
* ad
* ae
* be
* de
* ef
Three Letters:
* ace
* bad
* cab
* cad
* dab
* deaf
* fed
Four Letters:
* bead
* deaf
* face
Five Letters:
* badge
Six Letters:
* abcdef (the original word itself)
Let me know if you'd like to try making words with another set of letters!