Seize refers to a verb that describes an action, i.e. chocolate seizes when water is added, usually accidentally, during melting.
It stiffens, loses its gloss, and becomes lumpy and unworkable. Sometimes this can be fixed by stirring in some solid shortening or oil.
Chocolate will scorch if you melt it at too high a temperature, or "seize" and become thick and grainy if you add even a drop of cold liquid to it as it's melting.
Seize is pronounced "seez"