Any plant of the genus Agrimonia, of the rose family (Rosaceae). The name particularly denotes A. eupatoria, an herbaceous, hardy perennial that is native to Europe but is widespread in other northern temperate regions, where it grows in hedge banks and the borders of fields. A. eupatoria grows to about 120 cm (4 feet) tall and has alternate feather-formed leaves that yield a yellow dye. The oval leaflets, about 2-6 cm long, have toothed margins. The small, stalkless yellow flowers are borne in a long terminal spike. The fruit is a bur about 0.6 cm in diameter and bears a number of hooks that enable it to cling easily to clothing or the coat of an animal. (Encyclopedia Britannica)
Hemp-agrimony made the bees sing a drousy song.

E.H. Barker, Wanders by Southern Waters 286 (1894)

Agrimonia eupatoria has composite pinnate leaves composed of lanceolate, denticulate leaflets. Called eupatorium from Mithridates Euaptor, king of Pontus, who first used it (as is noted in Chapter 50, line 48). Eupatoria is an old name of Agrimony, as is Liverwort. The older spelling was Argemony, and Pliny calls it argemonia, from the Greek argemos, a white speck on the eye, which this plant was supposed to cure.
For sore of eyes, take this wort, which is named agrimony, and by another name garclive...

Apuleius 32.1.

Others say that agrimony is Papaver agremone, (from Hebrew argaman, red-purple). Or hemp-agrimony, a book name for Eupatorium cannabinum, a composite plant with dull red leaves. This is the eupatorium of Avicenne (bastard, Dutch, water, or hemp agrimony), which has composite leaves, three to five lobes lanceolate - "acumines," dentate, similar to those of hemp.
Eupatoria too enjoys the prestige of a royal discoverer. It has a ligneous stem, dark, hairy, and a cubit or sometimes more in height. The leaves, arranged at intervals, are like those of cinquefoil or hemp, and have five indentations along the edge; they too are dark and feathery.

Pliny 25.29.65

Agremone [somme call it Oenone, spomme Anthemis, somme Homonoia, as we should say Concord, somme Flos campestris, the Romans call it Liburnia or Concordailis, somme call it Pergalia, the French call it Corna] is wholly like unto wilde Poppie, but it hath a leafe divided like to Anemone, a flower on ye stalk of the Phoenician colour, but an head like to Paupauer Rhoeas, but somewhat longer...

Dioscorides 2.208

The other Agremone some call Artemone, somme Arselam, somme Sarcocolla, the Romanes call it Artemonia, & it is like to wilde Poppie in the leaves.

Dioscorides 2.208

Eupatorium [some call it Hepatorium, some Hepatitis, ye Romans Volucrum maius] is an herb like a shrub, putting out one rod, thin, woody, straight, black, rough, a cubit long, or rather more, but ye leaves jagged by distances, most commonly into 5 parts, or rather more, like to those of Quinquefolium or rather Cannabis, & those inclining to black, cut in by ye outsides like a saw... Some being deceived have called this Artemisia, for it is diverse, as we have shown.

Dioscorides 4.41

Hemp, or Cannabis -- Cannibus sativa or Eupatorium cannabinum (known as hemp agrimony) -- 1. This wort, which is named cannabis silvatica, and by another name hemp, is produced in rough places and against ways and hedges. 2. For sore of the breasts, take this wort cannavis silvatica, pounded with grease, lay it to the breasts; it removes the swelling; and if any gathering be there, it purges it away. 3. For a chill of burning, that is, a blistering or inflaming by cold, take fruit of this same wort, pounded with seed of a nettle, and soaked with vinegar; lay it to the sore.

Apuleius 116

The name appears in Platearius (13th century) as eupastoire and eupautoire; as eupatoire in the Grand Herbier (15th century) and in the Hortus Sanitatis.