'angular-splenial' is a modern compound formed from 'angular' + 'splenial'. 'Angular' originates from Latin 'angulus' meaning 'angle' (via Late Latin/medieval usage 'angularis'). 'Splenial' originates from New Latin anatomical usage 'splenium' (ultimately from Greek elements used in anatomical formation).

'Angular' entered English via Latin 'angularis' (from 'angulus') and Old French influence, yielding the adjective and later anatomical noun uses. 'Splenial' arose in New Latin anatomy (18th–19th century) to name a specific element of the lower jaw; the compound 'angular-splenial' is a later descriptive term in comparative anatomy and paleontology to refer to the fused element or unit composed of those parts.

Originally the separate terms referred to distinct bones or regions ('angular' and 'splenial'); over time the compound came to be used to name the fused or single element representing those parts in some taxa — i.e., from two separate bones to a recognized fused anatomical unit.