The Collaborative International Dictionary
In antis
In antis \In an"tis\ [L.] (Arch.) Between ant[ae]; -- said of a portico in classical style, where columns are set between two ant[ae], forming the angles of the building. See Anta.
Wiktionary
in antis
adv. (context architecture English) Between antae; said of a portico in classical style, where columns are set between two antae, forming the angles of the building.