sa'ei zei valsi zei-lujvo

x₁ is an onomatopoeia, a word that sounds like what it represents

Examples are "gurgle" or "hiss". See sa'ei, ki'ai, valsi

On affix form:

valsi: x₁ is a word meaning/causing x₂ in language x₃; (adjective: x₁ is lexical/verbal).
zekri: x₁ (event/state) is a punishable crime/[taboo/sin] to people/culture/judges/jury x₂.

zeiljvo: x₁ (text) is a Lojban compound predicate using the particle “zei”; with meaning x₂, arguments x₃, built from metaphor (tanru) x₄.
zejvo: x₁ (text) is a Lojban compound predicate using the particle “zei”; with meaning x₂, arguments x₃, built from metaphor (tanru) x₄.
zo si si zei fa'o: x₁ is a nonsense zei-lujvo using parts x₂, silly by standard x₃.

ci'o'ei: Convert arbitrary bridi to UI with the grammar of {sei} (deprecated in favor of «ui'ei»).
ci'oi: Converts following cmevla or zoi-quote into psychomime.
isku: x₁ is a sound represented by onomatopoeia x₂ (text) according to x₃ (experiencer)
ki'ai: Converts following selbri, cmevla, or zoi-quote into a nonce interjection/attitudinal.
mi'au: attitudinal: meow, miaow
snafu'ivla: x₁ is an onomatopoeic word meaning x₂ in language x₃, based on sound x₄ emitted by x₅
tai'i: Converts following cmevla or zoi-quote into phenomime.