The difference between homonyms and polysemes is subtle. Lexicographers define polysemes within a single dictionary lemma, numbering different meanings, while homonyms are treated in separate entries (or lemmata). Semantic shift can separate a polysemous word into separate homonyms. For example, "check" as in "bank check" (or "Cheque"), "check" in chess, and "check" meaning "verification" are considered homonyms, while they originated as a single word derived from chess in the 14th century. Psycholinguistic experiments have shown that homonyms and polysemes are represented differently within people's mental lexicon: while the different meanings of homonyms (which are semantically unrelated) tend to interfere or compete with each other during comprehension, this does not usually occur for the polysemes that have semantically related meanings. Results for this contention, however, have been mixed.