Emancholl is unusual among the forfeda in that its name describes its form rather than its sound or its plant gloss. The word means twinned hazel, referring directly to Coll, hazel, the fourth letter of Aicme hUatha in the original twenty letter alphabet, and to the doubled appearance of Emancholl's own shape, which repeats Coll's stroke pattern on both sides of the stemline rather than the single side the original letter uses. The name is, in effect, a scribe's note on how the character was built, preserved as its title rather than lost to later commentary.
The letter was devised to carry the sound ch, another gap opened by sound change between the period the core alphabet was cut and the period the forfeda were added. Its relationship to Coll is closer than any other forfeda's relationship to a core letter, which has led some readers to treat it less as a wholly new character and more as a deliberately marked variant of an existing one, though the manuscript tradition consistently lists it as a fifth, independent forfeda rather than folding it back into Aicme hUatha. The naming choice also shows that whoever coined the term understood the letter as a construction, a visible doubling of an existing sign, rather than as a shape arrived at independently and only later compared to Coll.
Sources Auraicept na n-Eces: The Scholars' PrimerGeorge Calder (ed.) with A Guide to OgamDamian McManus