Combine rhubarb, onion, raisins, sugar and vinegar. Cook until thick, about 25 minutes. As mixture thickens, stir frequently to prevent sticking.
Add spices; cook 5 minutes longer.
Pour, boiling hot, into sterlized pint jars, leaving 1/8-inch head space. Adjust caps. Process in a boiling water bath according to manufactures instructions. Makes about 4 pints. Excellent accompaniment with meats.