Definition of abactinal in English:

abactinal

adjective

Zoology
  • Designating the part or surface of an echinoderm or other radiate animal that is furthest from the mouth (as the upper side of a starfish); relating to this part.

Origin

Mid 19th century; earliest use found in Louis Agassiz (1807–1873), zoologist and geologist. From ab- + actinal.

Pronunciation:

abactinal

/əˈbaktɪnəl//aˈbaktɪnəl/