In finnish: "epäjärjestelmällistyttämättömyydelläänsäkäänköhän" 49 letters. This is a single word, and not a compound noun (don't make me translate it!). Compound nouns included, one can make reeeaaally long words:
You mean... one SINGLE word? Not compound??
Anyway, I'm not sure what's the longest word in Romanian. But I know that the word with most syllables that's not a chemistry thing has 9 syllables (telecomunicatiilor; te-le-co-mu-ni-ca-ti-i-lor), and it means "belonging to/of the long distance communications".
We don't have such long words in Romanian.

But on average, words are longer than in most European languages (discounting Germanic ones

), because we often add a couple of large suffixes at the end of each word in a sentence.
In fact, Romanian often is very different in this aspect from other Romance languages, as it uses an older, classical Latin system, not the Vulgar Latin one, meaning that it has A LOT less prepositions and articles and instead it makes those by adding terminations to the word.
Example: "Dau cartea fiului amicului fratelui meu" ->
.............."I give the book to the son of the friend of my brother", count the prepositions and articles in English and compare

)
If we count technical words, well, we have: GASTROPILORODUODENOJEJUNOSTOMIE, DIFOSFOPIRIDINNUCLEOTIDPIROFOSFATAZĂ, inonorificabilitudinationalitate, ELECTROMOTOSTIVUITORISTICA, etc.
The longest non-compound word is constantinopolitanilor", which means "belonging to/of the citizens of Constantinople".