BTW, you were talking about trained musicians, in the main. And I would expect the distinction between “song” and “tune” (AND “melody”!) to be more in evidence among that bunch. But how about the British nonmusician, or the self-taught? Do you find the same level of distinction between these words among that group?
Absolutely definitely not. Everyone calls any piece of music a “song”. I blame Apple. 
But then, the majority of the population, or so it seems, spell the neutral possessive pronoun as " it’s ". I don’t see why we should have to put up with something that’s just plain wrong simply because people who don’t know any better insist on perpetuating the error.
You aren’t making it up, at least in terms of the Greek ode.
Exerpted from Wiki, FWIW:
Greek odes were originally poetic pieces accompanied by symphonic orchestras. As time passed on, they gradually became known as personal lyrical compositions whether sung (with or without musical instruments) or merely recited (always with accompaniment). For some, the primary instrument of choice was either the aulos or the lyre…
A couple of points in the above - “symphonic orchestras” and “always with accompaniment” - were challenged with a call for citation. “Ode” tends to be translated as “song” in some dictionaries, but it seems it’s more accurate to say that the actual Greek word, oide, is a contraction of the usual word for “song”, aoide. Dunno how important that difference is.
They haven’t helped things, that’s for sure. Not to be a drudge, but I recall that using “song” as the default street term for all goes back well further into at least the last vestiges of the Gutenberg era.
Gah! When was that??!? The end of print as we know it? Have I missed it? 
Oh, you. Maybe I should have instead said, “the Gutenbergian Ascendancy”.
Just as an aside, am I the only one who finds the “Gutenberg Project”, a project to dsitribute e-books, to be almost unbearably ironic?
Not any more.
NO!!! Shirley!!!
There’s always the “ten thousand flies” argument. 
I presume you mean “ten thousand fly’s”. Grrr …
ok ill take tune as the melody, the music, the number, or could one say melody with rythmn but without singing?
more clearly to me is song just to be used when its sung
… thinking…
what about mouth music? making sopunds with the mouth, not real singing? 
like beatbox, ok i would not call that music at all, forget it
better example, a capella (how is that written in english?) background (the melody part not the words), isnt this sung tunes?
what about Puirt a beul, are these sung words?
anyway my first question is answered , song just when its sung
otherwise tune is a good word for what i call in german “lied”
The thing is you have things like Lumps of Pudding, that was an Irish song that they re made into Thus I stand like the Turk for the beggars opera. Although they share the same melody, are they played as the same tune? Do timing and meter change things or is that encompassed by the word melody too? The Moreen was a tune long before it became The Minstrel Boy, and if the tune became re-purposed again what would it be? Thomas Moore wrote many poems to go with existing tunes and the US national anthem is an example of such a recycling of tunes. Often parodies are written and the annotation will say something like "sung to the tune of… " To me it seems lyrics and the tune make a song, but it is useful to be able to talk about the parts with separate terms.
Some Puirt for German Whistler
Mary Anne Kennedy
Julie Fowlis
Colin Watson - a bit of pure drop.
Joy Dunlop - some more pure drop.
David
thats what i mean, the _pure drop_s what is it?
sung tunes?
so what is “Plainsong” ? and how does that fit in here ?
Look, just because you’re British it doesn’t give you carte blanche to correct my spelling day in and day out. And I’m a Statesider. I’m NOT going to spell it your way. So stop it. 
There’s a good question. I think of puirt à beul as pretty much characterised by nonsense vocables, sounds that aren’t even real words. But of course this isn’t always true. “Port” in this case means “tune”, and “à beul” means “by mouth”. To say puirt à beul are sung is accurate enough (although sometimes I might prefer “vocalised”), but because its purpose is as a vocal instrument for conveying dance tunes for dancing, even though it is sung I don’t think of it as a song, per se: to me songs are very much about the lyrics, and need not be danceable at all.
I suppose at this point it all depends on who’s talking. But I can say that as a convention, my trad friends and I say “puirt” or “port” for short when speaking of puirt à beul. We don’t call them “songs” for any reason. Odd thing is, no one told us to do that. It’s just natural and makes sense for us in the context of trad.
I do not recall anything other than the usage Ben is describing until I came across iTunes and discussion boards like this, at roughly the same time. I assumed that ‘song’ for ‘tune’ was a north American usage. I do recall hearing merkin musicians talking about toons long before that though, so was inclined to blame iTunes.
I notice that some psychologists writing for a more general readership do use ‘song’ for tune and wonder if, within their field, this is semantically correct in the same way that nano says it is within the NAF community. Also in the way that in the field guides birds have ‘songs’ and ‘calls’ even though they don’t use words.
Is the abruptness with which new posters are often corrected a response to it showing that they haven’t done much reading of older posts here before joining in ?
You find the term “Pure Drop” (no plural) mainly within the Irish tradition in reference to its real, fundamental core: essentially, the solo instrument. It’s very much an aesthetic term.
The words “pure drop” themselves refer to the product of distillation, so they’re quite appropriate in how they evoke the idea musically. 
iTunes? Ha. We were doing that way before iTunes, back when there were only turntables, needles, and LPs (yes, I’m that historical ). It was (and I expect may still be) a relaxed, informal colloquialism for musical pieces, and what in particular may be heard from the tracks of a recording. I’ve mainly heard this usage in reference to popular music: “Dude, put on some tunes.” If you’re insufferably hip, you say “tunage”.
I confess I’m not sure what has inspired this question. Could be I haven’t been paying attention.