Tip of the tongue (also known as lethologica) is the phenomenon of failing to retrieve a word or term from memory, combined with partial recall and the feeling that retrieval is imminent. The phenomenon's name comes from the saying, "It's on the tip of my tongue." The tip of the tongue phenomenon reveals that lexical access occurs in stages.

People experiencing the tip-of-the-tongue phenomenon can often recall one or more features of the target word, such as the first letter, its syllabic stress, and words similar in sound, meaning, or both sound and meaning. Individuals report a feeling of being seized by the state, feeling something like mild anguish while searching for the word, and a sense of relief when the word is found. While many aspects of the tip-of-the-tongue state remain unclear, there are two major competing explanations for its occurrence: the direct-access view and the inferential view. Emotion and the strength of the emotional ties to what is trying to be remembered can also have an impact on the TOT phenomenon. The stronger the emotional ties, the longer it takes to retrieve the item from memory.

TOT states should be distinguished from FOK (feeling of knowing) states. FOK, in contrast, is the feeling that one will be able to recognize⁠—from a list of items⁠—an item that is currently inaccessible. There are still currently opposing hypotheses in the psychological literature regarding the separability of the process underlying these concepts. However, there is some evidence that TOTs and FOKs draw on different parts of the brain. TOTs are associated with the anterior cingulate, right dorsolateral prefrontal cortex, and right inferior cortex while FOKs are not. FOKs can be assessed through memory-monitoring testing in which a test subject is asked to "estimate the likelihood" of recognizing when "prompted with a cue" or information that they previously failed to remember. This test aims to measure a test subject's accuracy of memory monitoring during the "memory extraction stage".

An occasional tip-of-the-tongue state is normal for people of all ages; however, it becomes more frequent as people age. TOT can be referred as an actual medical condition, but only when it becomes frequent enough to interfere with learning or daily life. This disorder is called anomic aphasia when acquired by brain damage, usually from a head injury, stroke, or dementia.

The tip of the tongue phenomenon has implications for research in psycholinguistics, memory, and metacognition.