Merriam-Webster's Collegiate Dictionary:
tricolored
tricorn
tricorne
tricornered
tricot
tricotine
trictrac
tricuspid
tricuspid valve
tricycle
tricyclic
tricyclic antidepressant
trident
tridentine
tridimensional
tridimensionality
triduum
tried
tried-and-true
triene
triennial
triennially
triennium
trier
trierarch
trierarchy
trieste
triestine
trifecta
trifid
trifle
trifler
trifling
trifluoperazine
trifluralin
trifocal
trifoliate
trifoliate orange
trifoliolate
trifolium
triforium
triform
trifurcate
trifurcation
trig
trigeminal
trigeminal nerve
trigeminal neuralgia
trigger
trigger point
trigger-happy
triggered
triggerfish
triggerman
triglyceride
triglyph
triglyphic
triglyphical
trigon
trigonal
trigonally
trigonometric
trigonometric function
trigonometrical
trigonometrically
trigonometry
trigram
trigraph
trigraphic
trihalomethane
trihedral
trihybrid
trihydroxy
triiodothyronine
trijet
trikala
trike
trikkala
trilateral
trilby
trilinear
trilingual
trilingually
triliteral
triliteralism
trill
triller
trillion
trillionth
trillium
trilobate
trilobed
trilobite
trilogy
trim
trim one's sails
trim size
