Manage one top conundrum having a mysterious meaning (5)
I believe the answer is:
runic
'a mysterious meaning' is the definition.
Although both the answer and definition are adjectives, I can't see how they can define each other.
'manage one top conundrum' is the wordplay.
'manage' becomes 'run' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'top' suggests taking the first letters.
The first letter of 'conundrum' is 'c'.
'run'+'i'+'c'='RUNIC'
'having' acts as a link.
Can you help me to learn more?
(Other definitions for runic that I've seen before include "Like some old characters" , "Using Norse letters" , "character hard to interpret" , "Of old magic symbols" , "Inscribed with ancient symbols" .)