Being very old, the cyclist may find them difficult (5)
I believe the answer is:
hills
'being' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'old the cyclist may find them difficult' is the wordplay.
I cannot quite understand how this works, but
'difficult' could be 'ill' (ill could historically mean difficult) and 'ill' is located in the answer.
This explanation may well be incorrect...
'very' is the link.
Can you help me to learn more?
(Other definitions for hills that I've seen before include "See 7" , "High terrain" , "Heights; tors" , "Elevations of land" , "Mounts" .)