The Collaborative International Dictionary
Fossil \Fos"sil\, a. [L. fossilis, fr. fodere to dig: cf. F. fossile. See Fosse.]
Dug out of the earth; as, fossil coal; fossil salt.
preserved from a previous geological age; as, fossil water from deep wells; -- usually implying that the object so described has had its substance modified by long residence in the ground, but also used (as with fossil water) in cases where chemical composition is not altered.
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(Paleon.) Like or pertaining to fossils; contained in rocks, whether petrified or not; as, fossil plants, shells.
Fossil copal, a resinous substance, first found in the blue clay at Highgate, near London, and apparently a vegetable resin, partly changed by remaining in the earth.
Fossil cork, Fossil flax, Fossil paper, or Fossil wood, varieties of amianthus.
Fossil farina, a soft carbonate of lime.
Fossil ore, fossiliferous red hematite.
--Raymond.
Wikipedia
Fossil wood is wood that is preserved in the fossil record. Over time the wood will usually be the part of a plant that is best preserved (and most easily found). Fossil wood may or may not be petrified. The study of fossil wood is sometimes called palaeoxylology, with a "palaeoxylologist" somebody who studies fossil wood.
The fossil wood may be the only part of the plant that has been preserved, with the rest of the plant completely unknown: therefore such wood may get a special kind of botanical name. This will usually include "xylon" and a term indicating its presumed affinity, such as Araucarioxylon (wood of Araucaria or some related genus), Palmoxylon (wood of an indeterminate palm), or Castanoxylon (wood of an indeterminate chinkapin).
Usage examples of "fossil wood".
Several pieces of the fossil wood were selected by the men to serve as whetstones.
There were also, on lower ground, ragged arches leading to a high-roofed cavern called Groyne, which had good clean air, although the inhabitants of Vakk thought the inhabitants of Groyne rather barbarous, chiefly because they were members of more lowly guilds, slaughterers, tanners, diggers of chert and clay and fossil wood.
In the higher beds are found, on the contrary, lignite and fossil wood, substances in which the quantity of carbon is infinitely less.
But Spargus insisted on Gibbs doing the coaling, seeing that he was a joiner and that coal is notoriously fossil wood.