Merriam-Webster's Collegiate Dictionary:
third party
third person
third rail
third reading
third ventricle
third world
third worlder
third-class
third-degree burn
third-dimensional
third-party
third-rate
third-rater
third-stream
thirdhand
thirdly
thirl
thirst
thirster
thirstily
thirstiness
thirsty
thirteen
thirteenth
thirtieth
thirty
thirty-eight
thirty-second note
thirty-second rest
thirty-thirty
thirty-three
thirty-two
thirty-twomo
thirtyish
thirtysomething
this
this side of
this-worldliness
this-worldly
thisbe
thistle
thistle tube
thistledown
thistly
thither
thitherto
thitherward
thitherwards
thixotropic
thixotropy
thm
tho
thohoyandou
thole
tholeiite
tholeiitic
tholepin
thomas
thomas ? becket
thomas ? kempis
thomas aquinas
thomas of erceldoune
thomism
thomist
thomistic
thompson
thompson submachine gun
thomson
thomson's gazelle
thong
thonged
thor
thoracic
thoracic duct
thoracically
thoracotomy
thorax
thorazine
thoreau
thoreauvian
thoria
thorianite
thorite
thorium
thorn
thorn apple
thornback
thornbush
thorndike
thorned
thorniness
thornless
thornlike
thornton
thorny
thoro
thorough
