'anil' originates from Spanish, specifically the word 'añil', which came via Portuguese 'anil', ultimately from Arabic 'an-nīl' (‘the indigo’), from Sanskrit 'nīla' meaning ‘dark blue’.

'añil' in Spanish and 'anil' in Portuguese were borrowed into English as 'anil' to denote the indigo dye/plant, and later the term underpinned the naming of 'aniline'; in chemistry, 'anil' came to denote an aniline-derived imine.

Initially, it meant the indigo plant or its blue dye; later, by extension in chemistry, it came to denote an aniline-derived imine (while the original dye/plant sense remains).