It loves most precipitous hill starts (5)
I believe the answer is:
oomph
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'loves most precipitous hill starts' is the wordplay.
'loves' becomes 'oo' (two O's - 'love' means zero in tennis).
'starts' says to take the initial letters.
The first letters of 'most precipitous hill' is 'mph'.
'oo'+'mph'='OOMPH'
Can you help me to learn more?
(Other definitions for oomph that I've seen before include "Informal energy or enthusiasm, usually in a girl" , "Sexy, exciting quality" , "sex-appeal" , "Enthusiasm - vigour - sex appeal" , "Get-up-and-go" .)