DEFINITIONS Please: Liberal, Progressive, Populist, Left, etc [View all]

Need some help here fleshing out a few definitions.
We all see how words lose meaning or are turned into pejoratives.

Given the current Elizabeth Warren hullabaloo,
and the Democratic Party fracture there is a need
for clear and well defined meaning for these terms.

When liberal, progressive, left, or Democrat are conflated none of these
words communicate much, and tend to muddy the discussion.

To support candidates and policy we need to speak clearly
or else run risk word twisting by detractors.

For example, Warren appears "Populist" but not very "liberal"
That is fine, no need to defend that.
But Attackers WILL point out she voted republican and point out
the racist, bigoted, sexist tendency of republicans.
Her detractors WILL exploit that gap and drive a wedge
between potential supports who may assume some mutually
agreed definitions which simply don't exist.

Words matter, and messages must be clear and unambiguous.
So what are OUR/the working definitions for:
Liberal, Progressive, Populist, Left, etc?