Being sloppy makes the French cross (3)
I believe the answer is:
lax
'being sloppy' is the definition.
(both can careless)
'the french cross' is the wordplay.
'the french' becomes 'la' (one of the French words for 'the').
'cross' becomes 'x' (X is cross-shaped).
'la'+'x'='LAX'
'makes' acts as a link.
(Other definitions for lax that I've seen before include "Not strict enough" , "Casual" , "Insufficiently strict" , "Not sufficiently careful" , "Slapdash" .)