Merriam-Webster's Collegiate Dictionary:
trippy
triptan
triptych
tripura
triradiate
trireme
trisaccharide
trisect
trisection
trisector
trishaw
triskaidekaphobia
triskele
triskelion
trismus
trisoctahedron
trisodium phosphate
trisomic
trisomy
trisomy 21
tristan
tristan da cunha
tristate
triste
tristearin
tristesse
tristeza
tristful
tristfully
tristfulness
tristimulus
tristram
trisubstituted
trisulfide
trisyllabic
trisyllable
trite
tritely
triteness
tritheism
tritheist
tritheistic
tritheistical
trithing
tritiated
triticale
tritium
tritoma
triton
tritone
triturable
triturate
trituration
triturator
triumph
triumphal
triumphalism
triumphalist
triumphant
triumphantly
triumvir
triumvirate
triune
trivalent
trivandrum
trivet
trivia
trivial
trivial name
trivialise
trivialist
triviality
trivialization
trivialize
trivially
trivium
triweekly
trna
troad
troadic
troas
trobriand
trobriand islander
trobriander
trocar
trochaic
trochanter
trochanteral
trochanteric
trochar
troche
trochee
trochlea
trochlear
trochlear nerve
trochoid
trochoidal
