Lady be Good is a Jazz Classic, and so the 11th chord generally indicates that the basic triad is formed (C, E, G) but also usually includes a seventh and a ninth. A C11 has a dominant note of F (the F making the 11th).

In some ways it is similar to a Csus chord, except the 4th is usually raised by a full octave to the 11th position.

In BiaB a C9sus is considered as an equivalent C11 chord (although this is not absolutely technically correct).

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