trefoil (n.)

• clover
• deuce-ace
• leash
• shamrock
• tercet
• ternary
• ternion
• terzetto
• three
• threesome
• tierce
• trey
• triad
• triangle
• tricorn
• trident
• trilogy
• trimester
• trine
• trinity
• trio
• triplet
• tripod
• triptych
• trireme
• triskelion
• triumvirate
• trivet
• troika