Definition of "smallage"

Chop the smallage exceeding small and put it in a good half hour before you are to take your posset from the fire: You are to season your Gruel with a little Salt, at the due time; and you may put in a little Nutmeg, and Mace to it.

1922, Eleanour Sinclair Rohde, A Garden of Herbs: Being a Practical Handbook to the Making of an Old English Herb Garden, page 123