Definition from Wiktionary, the free dictionary
Audio (US) (file)
- (transitive) To mark (as of sheep) by slitting the ear.
- (transitive, by extension) To specify or set aside for a particular purpose.
- You can donate to the organization as a whole, or you can earmark your contribution for a particular project.
to specify or set aside for a particular purpose
earmark (plural earmarks)
- A mark or deformation of the ear of an animal, intended to indicate ownership.
- (US, politics) The designation of specific projects in appropriations of funding for general programs.
- A mark for identification; a distinguishing mark.
- Money is said to have no earmark.
- A set of intellectual ideas […] have earmarks upon them, no tokens of a particular proprietor.
Coordinate terms 
- (US politics): phonemark
A mark of the ear of an animal
The designation of specific projects in appropriations of funding for general programs