Technically, according to the third edition of the American Heritage Dictionay, a shaman is “a member of certain tribal societies who acts as a medium between the visible world and an invisible spirit world and who practices magic or sorcery for purposes of healing, divination, and control over natural events” (AHD, 1992). The derivation of the word “shaman” is Russian, from Tungus saman, Buddhist monk, shaman, from Tocharian samene, from Prakrit samana, from Sanskrit sramenah, from sramah, religious exercise; you will note that shaman is ultimately Indo-European in origin (AHD, 1992). Although I realize that the word “shaman” is a loaded word, implying the ritual practices of the Tungus people, I do think that there is evidence of shamanic behavior in medieval Celtic literature.
Ann Ross describes the druids as “priests who do not seem to have differed so very basically from the shamans of the Finno-Ugric peoples” (Ross Pagan Celtic BritainChicago: Academy Chicago Publishers, 1967; repr. 1991. 80). Later she refers to the description of the chief druid of the king of Ireland, Mogh Ruaith, in the “Siege of Drum Damhghaire.” Mogh Ruaith is said to ask for his “dark gray hornless bull hide” and to wear a “white speckled bird skin head dress of fluttering wings” (Ross 1991, 83). Stuart Piggott, in his The Druids (New York: Thames and Hudson, 1975; repr. 1991) dissents from Ross’ opinion at one level, but describes the head dress and other shamanic similarities like the hoof-and-hide votive deposits as “from a very archaic substrate of belief” (188). I prefer a middle way, myself. To quote J. F. Nagy
Indeed, the Irish poet’s function as the proclaimer of truth who reveals the hidden has a definitely “shamanic” quality to it: That is, the fili knows, “sees,” and can communicate because he is regularly transported into the otherworld, or because he becomes possessed by otherworldly inspirational forces.
(From Nagy, J. F. The Wisdom of the OutlawBerkeley: University of California Press, 1985. 25.
Some of the behaviors that I would consider “shamanic” are the references to the rituals of the tarb fess (in Serglige Con Culainn, and Togail Bruidne Da Derga) and Imbas forosna. There are also intriguing references in Welsh medieval texts.
In the Serglige Con Culainn, or The Wasting Sickness of Cú Chulainn the hero lies in his sickbed, surrounded by the Ulaid in An Téte Brecc. At the same time, four kings are assembled in Emain Macha, where they hold the tarb fes, the “bull feast,” to determine the next king. The tarb fes is carefully described:
Is amlaid dognithe in tarbfes sin .i. tarb find do marbad & óenfer do cathim a satha día eóil & da enbruithi. & cotlud dó fón saith sin. & ór firindi do cantain do cethri druidib fair & atchíthe dó i n-aslingi innas ind fir no fígfaide and asa deilb & asa turascbail & innas ind oprid dognith (LU 3450-3454).
This is how that bull-feast used to be made: to kill a white bull, and for one man to eat his fill of its flesh and its broth, and to sleep after that meal; and for four druids to chant a spell of truth over him. And the form of the man to be made king used to be shown to him in a dream, his shape and his description, and the manner of work that he was doing.
(From Dillon, Myles. “The Wasting Sickness of Cú Chulainn.” Scottish Gaelic Studies VII (1953): 47-89. 56).
The result of the tarb fes is that one of the men surrounding Cú Chulainn, his foster son Lugaid, is chosen as the next king because he matched the vision of the tarb fes. This section of the Serglige is pretty clearly borrowed from the earlier text, Togail Bruidne Da Derga The Taking of Da Derga’s Hostle. (See Eleanor Knott ed. Togail Bruidne Da Derga Dublin 1936. 4). The two versions are almost identical.
The divinatory properties and procedures of the tarb fes
are strikingly similar to the divinatory ritual of imbas forosna described in the Sanas Cormaic , a ninth century Irish manuscript. In imbas forosni, or “knowledge that enlightens” a filifirst chews a piece of raw meat (don’t try this at home kids).
Imbas forosna reveals the thing that the fili wants to know and has to reveal. Itis thus that it is performed. The fili chews a morsel of raw pig, dog or cat and then puts it on the flagstone behind the door. He chants over the morsel and offers it to the idol gods. He calls them to him and does not leave [them?] the next day. He chants over his two palms and calls the idol gods to him lest his sleep be disturbed. He puts his two palms over his two cheeks and sleeps; he is watched lest he turn over or be disturbed by someone. Then is revealed to him whatever is going to happen to him in the next nine, eighteen, or twenty-seven days, or until the end of the period during which he can be at sacrifice.
(From Sanas Cormaic An Old-Irish Glossary. ed. trans. Kuno Meyer. Anecdota from Irish Manuscripts vol 14 Eds. O. J. Bergin, R. I. Best, Kuno Meyer, J. G. O’Keefe. Dublin: Hodges, Figgis & Co. Ltd, 1912. p. 64).
Were the Celts shaman? Yes. Maybe. I don’t know; I do think that there were rituals and beliefs about going to the otherworld. This is something I have only begun to read about, but you are welcome to my reading list, such as it is.