Line in amusing entertainment, maybe making one sort of cross (7)
I believe the answer is:
saltire
'one sort of cross' is the definition.
(saltire means a diagonal cross)
'line in amusing entertainment maybe' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'in' means one lot of letters goes inside another.
'amusing entertainment maybe' becomes 'satire' (satire is amusing).
'l' inserted into 'satire' is 'SALTIRE'.
'making' is the link.
(Other definitions for saltire that I've seen before include "flag - 8's? [SAINT ANDREW]" , "Heraldic cross" , "Diagonal cross (heraldry)" , "standard for Scots" , "Scottish cross" .)