Aldudénië is a poem lamenting the death of the Two Trees, composed by Elemmírë of the Vanyar, soon after the event. It was famous to all the Eldar, but never recorded.
Aldudénie is said to mean "lament of the Two Trees" and contains aldu, the dual of alda "tree".
The other element *dénie which obviously means "lament", is of problematic etymology since the intermedial "d" does not exist in Quenya (only the "ld" and "nd" are present). It might be some idiom of the Vanyarin dialect of Quenya.
Other similar Quenya word for lament isnainie from root NAY. Perhaps dénie derived from PQ *nayniê.