This study shows that the presence of a tip-of-the-tongue (TOT) state--the sense that a word is in memory when its retrieval fails--is used as a heuristic for inferring that an inaccessible word has characteristics that are consistent with greater word perceptibility. When reporting a TOT state, people judged an unretrieved word as more likely to have previously appeared darker and clearer (Experiment 1a), and larger (Experiment 1b). They also judged an unretrieved word as more likely to be a high frequency word (Experiment 2). This was not because greater fluency or word perceptibility at encoding led to later TOT states: Increased fluency or perceptibility of a word at encoding did not increase the likelihood of a TOT state for it when its retrieval later failed; moreover, the TOT state was not diagnostic of an unretrieved word's fluency or perceptibility when it was last seen. Results instead suggest that TOT states themselves are used as a heuristic for inferring the likely characteristics of unretrieved words. During the uncertainty of retrieval failure, TOT states are a source of information on which people rely in reasoning about the likely characteristics of the unretrieved information, choosing characteristics that are consistent with greater fluency of processing.