Merriam-Webster's Collegiate Dictionary:
triarchy
triassic
triathlete
triathlon
triatomic
triaxial
triaxiality
triazine
trib
tribal
tribalism
tribally
tribasic
tribe
tribesman
tribespeople
tribo-
triboelectric
triboelectricity
tribological
tribologist
tribology
triboluminescence
triboluminescent
tribrach
tribrachic
tribulate
tribulation
tribunal
tribunate
tribune
tribuneship
tributary
tribute
tributyltin
tricarboxylic
tricarboxylic acid cycle
trice
triceps
triceratops
trich-
trichiasis
trichina
trichinal
trichinize
trichinosis
trichinous
trichloracetic acid
trichlorfon
trichloroacetic acid
trichloroethylene
trichlorphon
tricho-
trichocyst
trichogramma wasp
trichogyne
trichologist
trichology
trichome
trichomonad
trichomonal
trichomonas
trichomoniasis
trichopteran
trichothecene
trichotillomania
trichotomous
trichotomously
trichotomy
trichromat
trichromatic
trichromatism
trick
trick or treat
trick-or-treat
trick-or-treater
tricker
trickery
trickily
trickiness
trickish
trickishly
trickishness
trickle
trickle-down
trickle-down theory
tricksiness
trickster
tricksy
tricky
triclad
triclinic
triclinium
triclosan
tricolette
tricolor
tricolored
