What is "grass oil"

Verbena \Ver*be"na\, n. [L. See Vervain.] (Bot.) A genus of herbaceous plants of which several species are extensively cultivated for the great beauty of their flowers; vervain.

Note: Verbena, or vervain, was used by the Greeks, the Romans, and the Druids, in their sacred rites.
--Brewer.

Essence of verbena, Oil of verbena, a perfume prepared from the lemon verbena; also, a similar perfume properly called grass oil. See Grass oil, under Grass.

Lemon verbena, or Sweet verbena, a shrubby verbenaceous plant ( Lippia citriodora), with narrow leaves which exhale a pleasant, lemonlike fragrance when crushed.