fossiilisilla

Fossiilisilla is not a standard Finnish word. It is commonly encountered as a mistaken inflection of the noun fossiili, which means fossil. The correct adessive plural form is fossiileilla, meaning on fossils or with fossils. The singular adessive form is fossiililla (on a fossil or with a fossil). The noun fossiili is a loanword derived from Latin fossilis.

Finnish nouns are declined for case and number by adding suffixes. For fossiili, the plural nominative is fossiilit, and the adessive plural is fossiileilla. This form follows regular patterns of Finnish inflection and is the form that should be used in formal writing and most contexts. The form fossiilisilla does not align with Finnish declension rules and is typically treated as a misspelling or nonstandard variant.

In practice, correct usage centers on fossiili and its inflected forms such as fossiililla (singular adessive) and fossiileilla (plural adessive). These forms are found in discussions of geology, paleontology and archaeology when describing the location or presence of fossils, for example in phrases referring to fossil beds or fossil-bearing materials.

See also: fossiili, fossiilinen, fossiilisto (related terms in the realm of fossils and fossilization).