Compouding is an unpredictable formational-transformational word formational type. The survey of compound words from the nineteenth century to the present is followed by a definition of the issue, which concerns (a) compounds as lexical items, (b) formation of compounds. The author also examines the list of compounds not included in the Slovar slovenskega knjižnega jezika. Among other things, she specifically treats the categoiral features of the base elements of the compound and of the compound as a whole. The analysis defines or, rather, confirms undivided spelling as a essential and sufficient condition for the compound word.