One who questions taboo briefly might sound puzzled (8,6)
I believe the answer is:
doubting thomas
'one who questions' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'taboo briefly might sound puzzled' is the wordplay.
'briefly' means to remove the last letter.
'puzzled' indicates an anagram.
'taboo' with its final letter taken off is 'tabo'.
'tabo'+'might'+'sound'='tabomightsound'
'tabomightsound' is an anagram of 'DOUBTING THOMAS'.
Can you help me to learn more?
(Other definitions for doubting thomas that I've seen before include "needed proof of life after death" , "sceptic" .)