As Mario noted, the 3rd against the 11th is a half-step dissonance - the 11th is the 4th scale degree.

So the 3rd degree is typically dropped from the 11th chord.

Instead of notating an 11th chord as an 11th such as C11, you'll often see it written as Gm7/C.

The chord is functionally the same as an 11th chord without the 3rd.

Using this notation ensures that the musician won't add the 3rd by mistake. Plus, it's a lot easier for the guitarist to figure out - they can leave the bass note out of the m7 chord, as long as the bass is playing it.

The same thing goes when voicing the 11th for a 4 part horn section - the horns play the m7, and with the root in the bass, you get a 11th chord.

-- David Cuny
My virtual singer development blog

Vocal control, you say. Never heard of it. Is that some kind of ProTools thing?