Depth? Start to relish one board game involving knight (8)

'depth?' is the definition.
(thesaurus)

'start to relish one board game involving knight' is the wordplay.
'start to' says to take the initial letters.
'one' becomes 'i' (Roman numeral).
'board game' becomes 'chess' (chess is a kind of board game).
'involving' means one lot of letters goes inside another.
'knight' becomes 'N' (chess abbreviation).
The first letter of 'relish' is 'r'.
'chess' enclosing 'n' is 'chness'.
'r'+'i'+'chness'='RICHNESS'