1. Operation on something past or preceding 
2. Action returned, or action backward

Derived forms: retroactions

• order Synentognathi
• order Taxales
• order Temnospondyli
• order Testacea
• order Testudinata
• order Testudines
• order Tetraodontiformes
• order Thecodontia
• order Therapsida
• order Thymelaeales
• order Thysanoptera
• order Thysanura
• order Tinamiformes
• order Torpediniformes
• order Tremellales
• order Trichoptera
• order Trogoniformes
• order Tuberales
• order Tubulidentata
• order Tulostomatales
• order Ulvales
• order Umbellales
• order Uredinales
• order Urodella
• order Uropygi