Okay, that's one reference to shields absorbing energy. But that doesn't mean it's their primary function. What they do is right there in the name -- the word "deflect" does not mean "absorb," it means "turn aside." As I said, it probably started out with the intent of being an asteroid deflector of the type recommended by the show's science advisors, something that would knock away approaching objects before they hit the ship (as suggested by the dialogue in "Where No Man" and "Corbomite"), before evolving into a more general, omnidirectional defensive shield. So the idea was that it would push material objects away, and that soon extended to energy weapons (or perhaps particle beams).
However, deflecting matter and absorbing energy aren't incompatible ideas. One way for a defensive layer to deflect an impact is by absorbing enough of its kinetic energy (say, by deforming on impact like a bike helmet or a car's crumple zone) to slow it down so that it doesn't penetrate the barrier and bounces off instead.
After looking at all references, it's fairly consistent that these terms all refer to the same system, not two separate ones.
As I've been saying all along.
The Motion Picture adds "forcefields" as another seperate system to the "screens and shields". Although I'm pretty sure nowadays they're all interchangeable terms for the magical forcefield (which was a big bubble when that was more practical to cheaply depict but are now skin-tight to ships) that stops our heroes being exploded when hit by enemy weapons.
As I keep saying, the terms "screen" and "shield" (with or without "deflector" preceding them) were interchangeable in TOS and TAS; it was only in TMP and (as
Maurice reminded me) TWOK that they were treated as separate systems, because Roddenberry apparently decided in the interim to invent a rationalization for the two terms as separate systems (maybe he got tired of fans asking him about the difference at conventions). However, according to Star Trek Script Search, the term "screen" has never been used as a term for a defensive field in any post-1982 production; after TWOK, it was abandoned entirely in favor of "deflector shield" as the standardized term, and the word "screen" was only used in reference to visual display devices.
As for "forcefield," interestingly, TNG-era shows used it to refer to alien defensive fields and interior shipboard security and containment fields, but never for the external deflector system.
Hey, so this gets us back to the original topic of the thread -- elements of TOS that are inconsistent with later series. One of those is using the term "deflector screen" instead of the later standardized term "deflector shield." Kind of like how TOS/TAS used an assortment of different terms for the Vulcan telepathic bond (mind-touch, mind-probe, mind-fusion, etc., with "mind-meld" used only twice in early season 3) before it was standardized as "mind-meld" in the movies and later shows thanks to
The Making of Star Trek using that term for it.
Turns out that TMoST may be the reason for the standardization here as well, since it favors the use of "deflector shield," though it adds the parenthetical that they're sometimes called "screens" as well (confirming that at the time, they were meant to be alternate names for the same system rather than two separate systems as they were retconned to be in
Phase II/TMP/TWOK). Similarly, the
Star Trek Concordance's lexicon entry on "deflectors" mostly calls them deflectors, deflector shields, or shields, with only one use of "deflector screen" in the entry.
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