vestige

Short definition from Wiktionary

Noun

1. 1
   A mark left on the earth by a foot.
2. 2
   A faint mark or visible sign left by something which is lost, or has perished, or is no longer present.
3. 3
   A vestigial organ; a non-functional organ or body part that was once functional in an evolutionary ancestor.
4. 4
   The remaining portion of a partially suppressed sideband.