Entry from British & World English dictionary
A European plant of the parsley family with yellowish-green flowers, formerly a widespread weed of cornfields.
- Genus Bupleurum, family Umbelliferae: two species, including B. rotundifolium, which is extinct in the wild in Britain
mid 16th century: from thorough 'through' + wax2 (because the stem appears to grow through the leaves).
Definition of thorow-wax in: