This article discusses a series of criteria that can be used to formulate research hypotheses regarding the lexicalization or the disappearance of neologisms created during the Middle Ages. In concrete, a previous analysis of neologisms used in certain translations of medical texts have revealed the large majority of borrowings from Latin, next to formations in the vernacular French language, like derivatives. Moreover, borrowings from Latin seem to lexicalize more easily. In this contribution, we would like to explore in particular the possible influence of morphological characteristics of the neologism on its lexicalization in the language. We pay special attention to criteria emphasized for Modern French by psycholinguistic studies, in order to discuss the way in which they can be applied to a corpus of medieval neologisms.