From Rick's find:

The nicknames were no mistake — Pound viewed himself as a brash risk-taker, while he considered Eliot’s reserve to be quietly subversive. True to form, Eliot even signed one of his letters “Tar Baby” (as in the story where the “Tar-Baby ain’t sayin’ nothin'”).

Pound, I guess, would liken Tom to a possum for he (Tom) partook of that animal's behavioral trait of feigning ignorance, sleep or death as a defensive tactic. 


On Sunday, October 11, 2015, Rickard A. Parker <[log in to unmask]> wrote:
On Sun, 11 Oct 2015 02:12:21 -0700, P <[log in to unmask]')">[log in to unmask]> wrote:

> So CR,  any idea why Pound nicknamed Eliot Ol' Possum?

I took 60% of this query (why Pound nicknamed Eliot Ol' Possum) and stuck it into Google. The first hit explained it:

The second hit was scholarly:
   The Dialect of Modernism: Race, Language, and Twentieth-century Literature
   By Michael North
   Old Possum and Brer Rabbit: Pound and Eliot's Racial Masquerade

   Rick Parker