(ornithology) Avian behaviour that occurs at night or in the twilight.

(UK, military) Full-time occupation in the military.

plural of active material

plural of active matrix

(computer science) A function that defines the output of a particular node in an artificial neural network on the basis of its inputs.

A book for children with interactive content such as games, puzzles, and pictures to be coloured in.

plural of activity book

(ichthyology) The use of light originating from the organism to illuminate the visual field to see into the field of vision.

Dated spelling of radioactive.

(obsolete, gay slang) Taking or preferring to take the insertive role in anal sex.