Monday Muddle: muster, mustard

muster: (verb) assemble (usually military troops) for inspection or for preparation for battle; (noun) assembly of troops for inspection or for a military exercise
Part of the expression “to pass muster”.

mustard: (noun) condiment made from seeds of the mustard plant; mustard plant
NOT part of the expression “to pass muster”.

“To pass mustard” is a grammatically correct and meaningful phrase, but it means something completely different from “to pass muster”.