Like the question says. We know the word Imzadi meaning something like Beloved.
But have we ever encountered any other word?
(Is it possible it's literally the least-developed (>0) language from a commonly recurring species?)
A thorough search of all Star Trek franchise television and film scripts shows that no other Betazoid word is uttered on screen (other than likely proper nouns such as "Rixx").
There may be plenty of instances in EU materials — such as the Peter David novel Imzadi or licensed video games — but these are non-canon at best.
Note that the Klingon, Vulcan, and Romulan languages were developed partly due to a desire by fans to converse in these languages (Klingon being the most developed, due to the efforts of linguist Marc Okrand at the time of STIII). I doubt there is much desire by anyone to converse in Betazoid. Their language has never been a plot point either — the focus being on their ability to communicate without speaking.
The d20 wiki lists some Betazoid names, which have meanings, which may come close to your answer:
Female Names: Deanna- Means: Nature's Beauty
Ania- Means: Spring blossom
Kestra- Means: Falling Leaves
Dalera- Means: Rainbow Gloranna - Means: Glorious Beauty
Algar - Means: Wise
Jensar - Means: Joy
Nikael - Means: Lucky
Kalos - Means: Envied
Rennan - Means: Gentle
Kalos - Means: Envied
In TNG S3E2 "The Ensigns of Command" Troi uses the word "S'smarith" when discussing the difficulties of learning the Sheliak language:
TROI: Attempted and failed. Actually, the fact that any alien race communicates with another is quite remarkable. We are stranded on a planet. We have no language in common, but I want to teach you mine. (she hold up his cup of tea) S'smarith. What did I just say?
PICARD: Cup? Glass?
TROI: Are you sure? I may have meant liquid, clear, brown, hot. We conceptualise the universe in relatively the same way.
PICARD: Point taken.
Technically we don't know that this word is Betazoid, or that is necessarily means "cup" as is implied, but consider that Troi says "we conceptualise the universe in relatively the same way", it seems logical that: