[Tex/LaTex] Left align definition for symbols in a LaTeX math equation

equationsmath-mode

I have an equation and want to have a 'where' block beneath it explaining the variables used. I would like to use something similar to the last example in this answer, but I would like the 'where' block to be aligned (as is, i.e. aligned in itself on the ':') at the left side of the text body — adapted to the surrounding text.

I would like to do so without leaving the math environment.

Here is my MWE:

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus ac velit dolor.
Nulla nunc dolor, commodo sed consectetur ac, dapibus malesuada odio.
Mauris porta libero eget nisi placerat quis bibendum tellus fermentum. It is therefore
possible to define the relationship
\begin{gather}
  x >> R + E,\\\notag
  \begin{split}
    \text{where } R &: \text{Racoon,}\\
    E &: \text{Elephant}
  \end{split}\hfill\mbox{}
\end{gather}
Sed suscipit tristique laoreet.
Nulla mi orci, rutrum sed dapibus sed, elementum nec lacus.
Phasellus id tellus mi, at rutrum justo. Nullam eget turpis justo, ullamcorper
pretium mauris.  It is therefore
possible to define the relationship
\begin{gather}
  x \gg R + E,\\\notag
  \begin{alignedat}{2}
    &\text{where} &\quad R &: \text{Racoon,}\\
    &     &E &: \text{Elephant}
  \end{alignedat}\hfill\mbox{}
\end{gather}
Sed suscipit tristique laoreet.
Nulla mi orci, rutrum sed dapibus sed, elementum nec lacus.
Phasellus id tellus mi, at rutrum justo. Nullam eget turpis justo, ullamcorper
pretium mauris.  It is therefore
possible to define the relationship
\end{document}

EDIT:
Based on the answer from daleif, I extended the MWE.

Best Answer

Here's a possibility, but what you want is not really nice, in my opinion.

\documentclass{article}
\usepackage{amsmath}

\newenvironment{where}[1][where]
 {\vadjust pre{\vskip-\belowdisplayskip}$\!\begin{aligned}\text{#1 }}
 {\end{aligned}$\\*[\belowdisplayskip]}

\begin{document}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus ac velit dolor.
Nulla nunc dolor, commodo sed consectetur ac, dapibus malesuada odio.
Mauris porta libero eget nisi placerat quis bibendum tellus fermentum. It is therefore
possible to define the relationship
\begin{gather}
x \gg R + E,
\end{gather}
\begin{where}
R &: \text{Racoon,}\\
E &: \text{Elephant}
\end{where}
Sed suscipit tristique laoreet.
Nulla mi orci, rutrum sed dapibus sed, elementum nec lacus.
Phasellus id tellus mi, at rutrum justo. Nullam eget turpis justo, ullamcorper
pretium mauris.  It is therefore
possible to define the relationship
\end{document}

enter image description here

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