| Stem | The form of the word to which inflectional suffixes are added; it thus excludes inflectional suffixes but includes thematic vowels and any modifications of the root caused by thematic vowels and/or inflectional suffixes, e.g. hǫnd- |
| Root | The semantic core of a word, stripped of inflectional endings, thematic vowels, and their effects on the root form, e.g. hand- |
| Thematic vowel | A vowel appearing between root and inflectional ending either in a word’s present form or in a reconstructed earlier form. Indo-European nouns, adjectives, and verbs can have thematic vowels, but in Old Norse it is only nouns and weak verbs that show their effect. |