The alphabet in use among the ancient Irish and some other Celtic nations prior to the ninth century.
“The oghams seem to have been merely tree-runes. The Irish regarded
the oghams as a forest, the individual characters being trees (feada),
while each cross-stroke is called a twig (fleasg).” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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