Dinosaur drops by for 1000m walk (4)
I believe the answer is:
trek
'walk' is the definition.
(I've seen this before)
'dinosaur drops by for 1000m' is the wordplay.
'dinosaur' becomes 'T Rex' (abbreviation for Tyrannosaurus Rex).
'drops' suggests deleting specific letters.
'by' becomes 'x' (2 by 4 is 2 x 4).
'for' means one lot of letters go next to another.
'k000m' becomes 'k' (I can't explain this - if you can you should give a lot more credence to this answer).
'trex' with 'x' taken out is 'tre'.
'tre'+'k'='TREK'
Can you help me to learn more?
(Other definitions for trek that I've seen before include "A long arduous walk" , "Difficult journey on foot" , "A long hard march" , "Slog" , "Long and difficult journey" .)