1) Something mentally supplied 2) Understood or implied meaning 
• (n.) The act of understanding, or supplying, something not expressed; also, that which is so understood or supplied.
Sub`au·di'tion noun [ Latin subauditio .] The act of understanding, or supplying, something not expressed; also, that which is so understood or supplied. Trench. 
subaudition 1. The act of understanding a word or thought that is implied but not actually expressed in speech or writing. 2. A word, idea, or thought understood by a hearer or reader that is implied but not expressed.
an act or instance of understanding or mentally supplying something not expressed. · something mentally supplied; understood or implied meaning.