Crossword Genius

Coating, one in battery? (5)

Ross

I believe the answer is:

layer

I'm a little stuck... Click here to teach me more about this clue!

'coating' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for layer that I've seen before include "See 22" , "Bed - hen" , "Lamina" , "Stratum; chicken" , "Single thickness and hen" .)

I've seen this clue in The Telegraph.
Want a hint initially instead of a full solution? Install my app