What is the longest word all of whose contiguous subsequences are words?

AMUSERS (7)

AMUSERS->AMUSER->AMUSE->AMUS->AMU->AM
MUSERS->MUSER->MUSE->MUS->MU
USERS->USER->USE->US
SERS->SER->SE
ERS->ER
RS

All words are in Webster's Third unless otherwise indicated.
Here are definitions for the less common words:

AMU: a unit of mass, formerly an acronym for Atomic Mass Unit [RH2]
MU: a Greek letter
SER: a unit of weight in India, a variant of SEER [RH2, SOED]
SE: a Chinese zither [SOED]
ERS: ervil [RH2]
ER: interjection used to express hesitation [RH2, SOED]

RH2 = Random House Unabridged Dictionary, Second Edition
SOED = Shorter Oxford English Dictionary