Oddly flat appeal with high confidence (5)
I believe the answer is:
faith
'confidence' is the definition.
(I've seen this before)
'oddly flat appeal with high' is the wordplay.
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
'appeal' becomes 'it'.
'with' means one lot of letters go next to another.
'high' becomes 'h' (this could be a standard abbreviation I've not previously seen).
The alternating letters of 'flat' are 'fa'.
'fa'+'it'+'h'='FAITH'
Can you help me to learn more?
(Other definitions for faith that I've seen before include "Strong belief in a supernatural power" , "Confidence" , "religion" , "Religious belief" , "Unshakeable belief" .)