Learner's definition of MUSTARD
a thick and spicy yellow or brownish-yellow sauce that is usually eaten with meat
a plant with yellow flowers, leaves that can be used for food, and seeds that are used in making mustard
a brownish-yellow color
see color picture on this page
(as) keen as mustard
cut the mustard
to be good enough to succeed or to do what is needed
She tried to join the soccer team, but she couldn't cut the mustard.
Now that we have computers, typewriters just don't cut the mustard anymore.