Dictionary.net

• A prefix to certain words.

1846 - Medical lexicon: a dictionary of medical science
By Robley Dunglison

• in comb. =Greek mesos middle, intermediate, as; -gaster, membrane attaching stomach to dorsal wall of abdomen; -lithic, of stone age between palaeolithic& neolithic; -phyll, inner tissue of leaf; -zoic, of second geological period.

1919 - The concise Oxford dictionary of current English
By Sir Augustus Henry