The name Quickbeam was given to him because he was hasty for an Ent. His Sindarin name, Bregalad, means "quick (lively) tree", derived from *breg- having to do with "violence, suddenness" and galadh, "tree". Quickbeam and Quicken are actual English names of the "rowan" or "mountain ash". It was not coincidental that "rowan" is mentioned in Quickbeam's song.
Noldorin
bregalad
masculine name. Quickbeam
Name of an Ent, translated “Quickbeam” in The Lord of the Rings (LotR/482), but elsewhere said to more literally mean “Quick (Lively) Tree” (PE17/82, RC/762). His name is most likely a combination of bregol “sudden” and galadh “tree”, probably influenced by Nan. galad (assuming the name is not itself Nandorin).
Conceptual Development: His name already N. Bregalad when it first appeared in Lord of the Rings drafts from the 1940s, with the same meaning (TI/419, WR/26).