Roots are Ithkuil's most basic semantic units. All Ithkuil formatives are derived from a limited number of roots. Each root consists of a cluster of 1–4 consonants (five-consonant clusters are also available, but remain without an assigned meaning). The current lexicon of Ithkuil can potentially consist of approximately 3,600 word roots, just over 1000 of which have been assigned definitions. From the root, word stems are formed by affixing the vocalic affix that indicates stem "pattern", stem type, "function" for the stem, and by stressing a particular syllable to indicate informal or formal designation.