Some compounds might be classified as derivations on the grounds that their second part does not appear as a separate word in contemporary language. The word älyniekka (a clever person, a genius) consists of äly (intellect) and niekka, and the second part (which comes from the Russian word ending “nik”) appears only as the second part of a handful of words. However, the word is best regarded as a compound, partly because it has not adapted to vowel harmony.
Many derivations ending with nen could be explained as compounds even though the second part does not occur as an independent word (or if it does, it has a different meaning). Words such as viisipaikkainen (five-seater) represent a very productive word type. They are often described in dictionaries as entries like the following (taken from a Finnish–English dictionary):
paikkainen (yhdyss); neli∼ auto (lentokone ym) a four-seater
This means that the “word” paikkainen (often presented as -paikkainen) occurs in compound words only (yhdyssanoissa), and it is explained only be explaining a particular example of its use, nelipaikkainen.
Although such dictionary entries can be very helpful, such words are more logically analyzed as derivations with two base words. Instead of treating viisipaikkainen as a compound of viisi and paikkainen, we can regard it as a derivation with suffix inen and with two base words, viisi and paikka. Wecan think that the logical base word is the open compound viisi paikkaa (five seats), but in the compound context, the first word appears in the compositive form (if it differs from the dictionary form) and the second one in the dictionary form: viisipaikka.
This analysis is more natural, since there many compounds with a structure like viisipaikka, existing as independent words. For example, harmaaparta (gray-bearded), from harmaa (gray) and parta (bear), is a synonym for harmaapartainen, just stylistically different.