The Nine Inch Nails song Dead Souls has the line
“Conquistadors that took their share”.
I have not heard that in another song before.
There’s plenty in Gilbert and Sullivan songs…
“… with many simple facts about the square of the hypoteneuse.” from Pirates of Penzance You gotta admit, you don’t find “hypoteneuse” much outside of math class or The Wizard of Oz
Connubially: from The Mikado
The other Bonzo posts reminded me of my favorite song of theirs, Keynsham, which features the word “Hexachloraphene”
The Beatles. “Hey, Bungalow Bill, what did you kill? Bungalow Bill.”
My entry is sycophants. I think it’s a Joan Jett and the Blackhearts song, but I could be wrong. “…and the sycophants who like to make romance to the ugly sound of them telling you that you’re wonderful and you pretend…”
Paul Simon has “Kodachrome.”
The musical “Candide” has “What a day, what a day for an auto-da-fe”
Except the Procol Harum tune titled “Conquistador,” which uses the word about once per verse. 
In Cake’s “Hem of Your Garment” the line “I am intrinsically no good” begins every verse.
And in the Dropkick Murphy’s “Spicy McHaggis Jig” it uses the term “schlong” musically.
I don’t know how big of a Dan fan you are, but pretty much every one of their songs would qualify for this thread. This band probably has the greatest vocabulary in rock (The Decemberists might come in at second place.)
From “Cry Me a River”: "Told me love was too plebeian/Told me you were through with me, an’… ".
That big internet hit from Tism, of a few years back, had a couple of very uncommon words: Everyone else has had more sex than me.
Our lives have to die
Of that there’s no help
My favourite way to end them
Is the orb-weaver spider’s whose pedipalp
Enters the female pudendum.
(Flash animation, music, Nothing nasty, just animated bunnies reporting in their chests the number of times they had sex. Still, the lyrics are not NSFW)
Try Nirvana’s “Radio Friendly Unit Shifter” or Dirty Pretty Things’ “Blood Thirsty Bastards.”
Sorry Jackmannii,
–Mel Brooks, The Inquisition
I think the Indigo Girls’ song Closer To Fine might qualify here. It contains: insatiable, definitive, “a poster of Rasputin” and prostrate.
Their self-titled debut album is pretty wordy in general, and I was kind of impressed with some of the unexpected phrasing even with fairly common words.
Ahhh, yes, good old Nine Inch Nails – recorded that song way back in 1965. Way before Joy Division 
Tom Lehrer, “Vatican Rag”:
get in line in that processional
step into that small confessional
…
2-4-6-8.
time to transsubstantiate!
And of course, the song repeatedly uses the word “genuflect.”
Blondie, “Accidents Never Happen”:
Like the Magi on a hill
I can divinate your presence from afar
This possibly deserves its own thread, but you guys should check out the World’s Hardest Lyrics Quiz.
It’s 26 song lyrics from Top 30 songs between 1965 and 1989. Each lyric consists of just one word, and all would be worthy mentions in this thread.
Not to mention the Smashing Pumpkins’ “Annie-Dog.”
I have contributions to add from my favourite band, The Weakerthans:
They also have a song about penguins and Antarctica. I could probably keep quoting them all day.
God, I love me some Weakerthans. 
Yes, that’s why I said the point stands. Carry on.
On this board, you spell that “scilla”? Pray for me, St. Pollykarp!
There are plenty of examples in Rush lyrics:
“Spirit Of Radio”, first line:
Begin the day with a friendly voice, a companion unobtrusive
“Vital Signs”, towards the end:
Everybody need reverse polarity.
“Between The Wheels”, beginning of song:
Soaking up the cathode rays
“Freewill”, middle of song:
All preordained