Worryingly, car heavy to start underfoot (4)
I believe the answer is:
arch
'worryingly car heavy to start underfoot' is the definition.
I can't judge whether this definition defines the answer.
'worryingly car heavy to start' is the wordplay.
'worryingly' is an anagram indicator (letters are disturbed or worried).
'to start' suggests taking the first letters.
The first letter of 'heavy' is 'h'.
'car' is an anagram of 'arc'.
'arc'+'h'='ARCH'
Can you help me to learn more?
(Other definitions for arch that I've seen before include "Shrewd; bridge" , "Affectedly playful like senior angel" , "Curve of the foot" , "Foremost" , "Roguish, teasing" .)