Also found in: Dictionary, Thesaurus, Medical, Encyclopedia, Wikipedia.
1. A hypothetical extinct animal that is believed to be the evolutionary connection between man and ape. Scientists will never fully understand the evolution of man until they find the missing link.
2. Something that is significantly, noticeably absent, often because its presence would be helpful or beneficial. Participation is the missing link in your grade, so I would suggest speaking up in class going forward. I think that chlorine is the missing link in this experiment.