itso = very (adverb) (some things Google found for "itso": a common term; Itso storage bins; ITSO is an acronym for International Telecommunications Satellite Organization; ITSO is the acronym of IBM's International Technical Support Organization; ITSO or Integrated Transport Smartcard Organisation defines smart ticketing specifications in the UK; nickname for Bulgarian masculine name Hristo)
Word derivation for "very" :
Basque = oso (very, entirely)
Finnish = erittäin (very, extremely)
Miresua = itso
This will be a useful word to have. I found it funny that that itso, with a space inserted becomes "it so", which seems a weirdly reasonable word for very. In addition, itso is a good mix of the Basque and Finnish words, containing all three letters that occur twice.
This word is shorter than the average length of the Basque and the Finnish words, but easily within my rules. As Miresua is an agglutinative conlang language, I'll have plenty of long words.