A lemma is one of two things with regard to languages. In linguistics, it is a word as it is presented in a dictionary or in a citation. In psycholinguistics, it is the conceptualization of a word before it has been given a sound.
The linguistic lemma is a word without any morphological changes made to it. An example is the word ‘go.’ The dictionary form of ‘went’ is still ‘go,’ as it is for ‘going,’ ‘goes’ and ‘gone.’ Some words are regular, like the verb ‘fish’ or the noun ‘cat,’ but others are irregular and this sometimes causes confusion with regard to that word’s lemma. The lemma of ‘we,’ ‘my,’ ‘mine’ and ‘ours’ is ‘I.’
Each lemma consists of morphemes made up of at least one phoneme. Each morpheme is a meaningful fragment of a word. Some of these can act as individual words, while others only work when combined with another morpheme. It is possible, therefore, for certain lemmas to be created out of more than one independent morpheme; for example, ‘bathhouse.’
The lemma should not be confused with the stem word. A word stem is the part of a word that does not change as the word runs through its various forms when inflected, put into cases, numbered or gendered. Often the stem and the lemma can be the same. In English, words like ‘wait’ and ‘run’ are both lemmas and stems, but other words like ‘I’ and ‘eat’ are not, because the basic structure of the word completely alters during morphology.
Depending on what language a person speaks, a lemma can come in different forms. Latin and Greek place the main entry word in the first person singular; Arabic, on the other hand, cites words in the third person masculine form. In English, French and German, the verb is put into the infinitive form.
In psycholinguistics, the lemma is defined as the concept of a word. For example, in 1780, British jurist Jeremy Bentham wanted to coin a word that could be used to describe things or organizations that existed between several nations. In thinking of this concept, he was creating a lemma. Later on, he decided to combine 'inter' with 'national' to create ‘international,’ although he then apologized for its inelegance.
The process of turning a thought into a new word is called lexicalization. This process has a number of stages including conceptualization, formulation and execution. The creation of the lemma falls into the conceptualization phase where the idea of the word is defined, but the letters and sounds attributed to voicing it are still unknown.