Half of gold bike, it's covered in sand (4)
I believe the answer is:
gobi
'sand' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'half of gold bike it's covered' is the wordplay.
'half of' means to take half the letters.
'gold' becomes 'gilt' (synonyms).
'bike' becomes 'ob' (I am not sure about this - if you are sure you should believe this answer much more).
'it's covered' means one lot of letters goes inside another.
'gilt' with half the letters taken is 'gi'.
'gi' going around 'ob' is 'GOBI'.
'in' is the link.
Can you help me to learn more?
(Other definitions for gobi that I've seen before include "vast arid expanse" , "barren tract" , "Sandy area" , "Area of sand" , "Mongolian/Chinese desert" .)