1.  costmary(n = noun.plant) alecost, balsam herb, bible leaf, chrysanthemum balsamita, mint geranium, tanacetum balsamita - tansy-scented Eurasian perennial herb with buttonlike yellow flowers; used as potherb or salad green and sometimes for potpourri or tea or flavoring; sometimes placed in genus Chrysanthemum;
is a kind of herb, herbaceous plant
has parts: costmary
is a member of genus tanacetum, tanacetum

2.  costmary(n = noun.food) - leaves used sparingly (because of bitter overtones) in sauces and soups and stuffings;
is a kind of herb
is a part of alecost, balsam herb, bible leaf, chrysanthemum balsamita, costmary, mint geranium, tanacetum balsamita

   A garden plant (Chrysanthemum Balsamita) having a strong balsamic smell, and nearly allied to tansy. It is used as a pot herb and salad plant and in flavoring ale and beer. Called also alecost. [1913 Webster]

costmary, n. (pl. -ies) an aromatic composite plant, Balsamita major, formerly used in medicine and for flavouring ale.

Etymology:
OE cost f. L costum f. Gk kostos f. Arab. kust an aromatic plant + (St) Mary (with whom it was associated in medieval times)