In linguistic morphology, an uninflected word or simple word has no affixes indicating declension or conjugation.
Verbs are uninflected in the infinitive ("to love") and the future tense ("will love"), but are inflected in the past tense ("loved"). They are also inflected in the third person singular with the "-s" affix ("she loves", "it seems", "the old man still walks every day").
In the strict sense, only words which cannot be inflected at all should be called uninflected words, which include all the parts of speech called particles, such as sentence connectors, prepositions, sentence substitutes, interjections, conjunctions, etc, none of which can be inflected under any circumstances, unless they change to nouns, participles, etc., as in "ifs and buts", or "humming and hawing".
In many inflected languages, such as Greek and Russian, some nouns and adjectives of foreign origin are uninflected; for instance, the name Abraam in Greek (from Hebrew), the modern Greek word mple (French bleu), the Italian word computer, and the Russian words kenguru (kangaroo) and pal'to (coat).