“DEADHEADED” is a valid word.

aheadhaving the leading position or higher score in a contest
addedmake an addition (to); join or combine or unite with others; increase the quality, quantity, size or scope of
aahedexpress admiration and pleasure by uttering `ooh' or `aah'
hadedhave or possess, either in a concrete or an abstract sense

deadpeople who are no longer living
headthe upper part of the human body or the front part of the body in animals; contains the face and brains
deeda legal document signed and sealed and delivered to effect a transfer of property and to show the legal right to possess it
heedpaying particular notice (as to children or helpless people)
dadaan informal term for a father; probably derived from baby talk
hade
haed

hadhave or possess, either in a concrete or an abstract sense
dadan informal term for a father; probably derived from baby talk
aahexpress admiration and pleasure by uttering `ooh' or `aah'
adda condition (mostly in boys) characterized by behavioral and learning disorders
aha
dee
hae
dahthe longer of the two telegraphic signals used in Morse code
edh

hea very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas)
ah
ha(astronomy) the angular distance of a celestial point measured westward along the celestial equator from the zenith crossing; the right ascension for an observer at a particular location and time of day
eh
dea Mid-Atlantic state; one of the original 13 colonies
edimpotence resulting from a man's inability to have or maintain an erection of his penis
ada public promotion of some product or service
ae
aaa dry form of lava resembling clinkers

DEADHEADED