Make a silly mistake ignoring fine mess (3)
I believe the answer is:
goo
'mess' is the definition.
(goo is a messy substance)
'make a silly mistake ignoring fine' is the wordplay.
'make a silly mistake' becomes 'goof' (goof can mean to blunder).
'ignoring' is a deletion indicator.
'fine' becomes 'f' (abbreviation).
'goof' with 'f' taken out is 'GOO'.
(Other definitions for goo that I've seen before include "Sticky stuff or sickly sentiment" , "mud, for example" , "Sticky and slimy stuff" , "Sticky substance (sl.)" , "syrup" .)