pitkittäisistä
Pitkittäisistä is the elatiivin monikko form of the Finnish adjective pitkittäinen, which means longitudinal or spanning along the length. In Finnish, adjectives of the -inen type decline like nouns, and the elatiivin (elative) plural form ends with -isistä. Thus pitkittäisistä translates roughly to “from the longitudinal ones” or “of the longitudinal ones,” depending on the context.
Grammatical overview is useful for understanding its usage. The base adjective pitkittäinen has several plural forms:
Usage and contexts. pitkittäisistä is common in scientific, statistical, and technical Finnish when referring to multiple
See also. Finnish grammar and declension of adjectives; longitudinal data and longitudinal studies in science; related
In sum, pitkittäisistä is a technical inflected form used to express origin or relation to longitudinal items