Crossword Genius

Back runner losing head after tip (7)

Ross

I believe the answer is:

endorse

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

'tip' is the definition.
Although both the answer and definition are verbs in their base form, I cannot understand how they can define each other.

'back runner losing head' is the wordplay.
'back' becomes 'end' (I've seen this in other clues).
'runner' becomes 'horse' (a race horse).
'losing head' means to remove the first letter.
'horse' with its first letter removed is 'orse'.
'end'+'orse'='ENDORSE'

'after' acts as a link.

Can you help me to learn more?

(Other definitions for endorse that I've seen before include "Docket" , "Support (with signature)" , "Express approval" , "Favour" , "Publicly approve" .)

I've seen this clue in The Telegraph.
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