How to substitute for mustard seed<br>Use prepared horseradish to add spice. Prepared horseradish is made by combining ground horseradish with vinegar, and sometimes other spices, to form a sauce. You can get it from your local supermarket.
Mustard seed has other substitutes than just horseradish.
( z1 substitute :ARG1 ( z2 mustard :mod ( z3 seed ) ) :ARG2 ( z4 horseradish :mod ( z5 just ) ) :mod ( z6 other ) )