Our aim is to study the common points and differences between two atypical non predicative adjectives "autre" and " second", often assimilated by dictionaries. The first part is devoted to the examination of the characteristics common to both these adjectives at syntactic, morphological and semantic levels. Secondly, the mainly semantic properties differentiating "autre" vs "second" are detailed, such as the methods whereby they construct the reference of their NP and the types of nouns that they select.