Popular line in board game is such a wonder (8)
I believe the answer is:
chinless
'such a wonder' is the definition.
I can't tell whether this defines the answer.
'popular line in board game' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'line' becomes 'l' (used when specifying particular lines from a poem).
'in' means one lot of letters goes inside another.
'board game' becomes 'chess' (chess is a kind of board game).
'in'+'l'='inl'
'inl' put into 'chess' is 'CHINLESS'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for chinless that I've seen before include "Without outstanding feature" , "(Of a "wonder") looking feeble and indecisive" , "Like some Hooray Henries" , "Lacking strength of character" , "Lack of courage, being without mandible" .)