"Elasticity of marginal utility of consumption ( μ ) with respect to utility." (Green Book quote)? In the Green Book (page 97) it is stated "the elasticity of marginal utility of consumption (μ) with respect to utility".

What is it? Is it an error ? I always heard of the elasticity of the marginal utility with respect to consumption...
Mere googling leads me to find a bunch of references about elasticity of marginal utility. 

Here Professor Acemoglu defines the elasticity of marginal utility as the inverse of the intertemporal elasticity of substitution (pagg. 17-18).

Here you can find a question analogous to yours together with an answer explained in an easier way than Acemoglu's lecture. 

If you are interested in something more empirical, have a look here: it is a paper by David Evans about the empirical estimation of elasticity of marginal utility in OECD countries.

Hope this is enough. If you have other questions, please ask