Sort of tap badly lapsing prior to completion (6)
I believe the answer is:
spinal
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for spinal that I've seen before include "Type of column" , "of a vital column" , "sort of column" , "Relating to the backbone" , "Member of dock family with edible stems" .)