Verne novel about Nemo's second appearance (6)
I believe the answer is:
veneer
'appearance' is the definition.
(I've seen this before)
'verne novel about nemo's second' is the wordplay.
'novel' indicates anagramming the letters (letters in a new or novel order).
'about' means one lot of letters goes inside another.
'nemo's second' becomes 'e' (2nd letter of 'nemo').
'verne' is an anagram of 'vener'.
'vener' going around 'e' is 'VENEER'.
(Other definitions for veneer that I've seen before include "Finish" , "False front" , "Mask; gloss" , "Superficial polish" , "Thin wooden facing" .)