埋もれ木に花が咲く
(Umoregi ni hana ga saku; “Flowers blooming on a buried tree”)

Definition:

Unexpectedly returning to fame, wealth, power, etc. after an extended time of obscurity, exile, or general misfortune. Just as a tree that has fallen and sunk into the earth is assumed to be dead, we assume that the career of someone who has fallen out of the public eye is over. Regaining the spotlight is akin to the fallen and buried tree suddenly sprouting leaves and flowers again.

Breakdown:

Right-to-left again! Our governing verb is 咲く (saku), “to blossom.” The particle が (ga) marks the noun 花 (hana, “flower”) as the subject of this verb. The particle に (ni) here marks location or something like giving – “to” in the sense of “unto,” if you will. And the location or recipient of the flowers is 木 (ki), “tree,” modified by the verb 埋もれる (umoreru), “to be buried/covered,” in prenominal form. Some dictionaries translate umoregi as “bogwood” or “bog oak,” although it hardly has to be actual oak.

Notes:

In related sayings, the buried tree may be exchanged for an old tree (老い木; oiki) or a withered tree (枯れ木; kareki). Some versions of these may elide the particle が.

The saying appears to be derived from a passage in the Tale of the Heike.

Example sentence:

「もう死んだかと思っていた作家が、二十年ぶりに傑作を出すとは、埋もれ木に花が咲いたんだね」

(“Mou shinda ka to omotteita sakka ga, nijuunen buri ni kessaku wo dasu to wa, umoregi ni hana ga saitanda ne.”)

[“For an author – who I thought was maybe dead – to put out a new masterpiece after twenty years… it’s like flowers blooming on a fallen and buried tree.”]