Crossword Genius

Very old, hot-headed complaints (5)

Ross

I believe the answer is:

hills

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

'very old' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'hot-headed complaints' is the wordplay.
'hot-headed' becomes 'h' (this might be a standard abbreviation I've not previously seen).
'complaints' becomes 'ills' ('ill' can be a synonym of 'complaint').
'h'+'ills'='HILLS'

Can you help me to learn more?

(Other definitions for hills that I've seen before include "Elevations of land" , "Mounts" , "Heights; tors" , "High terrain" , "See 7" .)

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