In psychology "Lexical leakage", as coined by Donald P. Spence, is not when the wrong word has been used, such as in the aforementioned Freudian Slip, but rather when the speaker subconsciously selects related words which tend towards a recuring theme throughout the discourse. These words provide information about "underlying needs, drives, or bodily states" without changing the meaning of what is being said.
For example, Spence cites controlled clinical studies of patients having biopsies to test for cervical cancer which indicated that those who tested positive had used the word death (and similar) during conversation with the clinicians prior to diagnosis significantly more often than those patients who subsequently tested negative.