-iainen

Etymology
. The suffix is spelled inconsistently as either or  depending on the root word.


 * is the original form of the suffix, while the former contains a preceding -i- (including those that derive from an underlying -e-), with the -j- not spelled as a result. In the past, a similar kind of vacillation occurred in the spelling of derivatives, although they eventually settled into a spelling in which the -j- was always spelled (, pro ). However, that development did not extend to this suffix, as its origin had by then been forgotten.
 * A regular derivative of many verbs would have a long vowel, as it is part of the stem; thus, should more correctly be . The shortening may be by analogy.
 * The use of the suffix in diminutive, often vulgar, nouns, such as those for insects, appears to follow the example of, , but may have also served as an inspiration.