Alliteration often uses words that are unrelated, just similar in their initial sounds. However, alliteration is also present in different forms of reduplication where a word is repeated as such or in different inflected forms or as derivations.
Phrases that consist of different forms of the same word are often used, e.g. aika ajoin (from time to time) and päästä päähän (from one end to the other, literally: from head to head). Lack of prepositions makes such expressions more alliterative than their English equivalents.
Finnish, like many languages, uses expressions like kuningasten kuningas (king of kings) and valheiden valhe (lie of lies). This international traditional type of phrases is in productive use in Finnish especially for names of properties, such as tyhmyyksien tyhmyys (stupidity of stupidities). The meaning is normally just emphatic. Although “king of kings” may originally have been seen as referring to a king (ruler) that rules kings (lower-ranking rulers), “Song of songs” is just a great song, not a song consisting of songs. Incidentally, this book of the Bible is called Laulujen laulu (song of songs) in the modern Finnish translation, but the traditional name is Korkea veisu (high song).
A similar construct is used for adjectives with the genitive singular, often written as a compound, e.g. suuren suuri or suurensuuri (very big, “big of big”), uudenuusi (brand new, “new of new”).
Phrases with stem reduplication, with the same word stem in two consecutive words, is also common. For example, hän juoksi juoksemistaan has a form of the verb juosta : juokse- (to run) and its noun derivative juokseminen : juoksemisen (running), so a very literal translation is “he/she ran of his/her running” and the meaning is “he kept running”. A longer version of this phrase type is hän juoksi juoksemasta päästyään, literally “he ran after getting out of running”.
Other examples of stem reduplication are hyvän hyvyyttään (for the goodness of his/her heart, literally “of his/her goodness of good)” and kysymällä kysyin (I intensively asked, literally “by asking I asked”). Generally, the adessive of the III infinitive, used together with another form of a verb, intensifies the meaning of that word. There are some exceptional meanings, too; e.g. tekemällä tehty (“by doing done”) does not simply refer to intensive doing but to something artificial, made up.
A more modern, and more colloquial, use of reduplication is the formation of a compound word by simple repetition. For example, kirjakirja means the same as kirja (book), but with emphasis on being “a real book” or “a genuine book”. It might even be used for a printed book as opposite to e-books and other digital publications, so the reduplication changes the meaning. Similarly, ruokaruoka might refer to “real food” as opposite to fast food or snack.