What's the longest sequence of words you can make, beginning with any word and adding one letter at a time, if each step must also be a word?
If you can add them only at the end, a computer search outputs the dubious:
co
com
comp
compo
compos
compose
composer
composers
Adding letters only at the beginning I get the equally doubtful:
es
hes
shes
ashes
lashes
plashes
splashes
If you add can add letters on either end, I found this valid 10-letter sequence:
I
in
tin
ting
sting
siting
sitting
slitting
splitting
splittings
My personal favorite, allowing rearranging letters, yields this whopping 15-letter series:
I
it
tie
rite
irate
attire
cattier
interact
intricate
recitation
ratiocinate
ratiocinated
accreditation
contraindicate
contraindicated
The above answers found using a python, and the GNU aspell dictionary. Words containing ', -, or capital letters were removed.