What is an Outside Word™?

Question

_{In the spirit of the What is a Word™/Phrase™ series started by JLee, a special brand of Phrase™ and Word™ puzzles.}

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If a word conforms to a special rule, I call it an Outside Word™.
Use the examples below to find the rule. I have made a mistake with a few of the words, so I've marked them with an "(E)" for error, while leaving them in so as not to invalidate Deusovi's correct answer.

Outside Words™	Not Outside Words™
FEED	STARVE
HEN	ROOSTER
DIRE	TIRE
SEND	SENT
SQUISH(E)	SQUASH
GREEN	BLUE
HEX	CURSE
WIND	WAND
SEEDS	SESAME
RIDDLE(E)	PUZZLE
INSIDE	OUTSIDE
SHORE	BEACH
OZ	WIZARD
DEODORIZE	STINK
HOW	TO
PROGRAM(E)	CODE
REP	REPUTATION

And, if you want to analyze, here is a CSV version:

Outside Words™,Not Outside Words™
FEED,STARVE
HEN,ROOSTER
DIRE,TIRE
SEND,SENT
SQUISH(E),SQUASH
GREEN,BLUE
HEX,CURSE
WIND,WAND
SEEDS,SESAME
RIDDLE(E),PUZZLE
INSIDE,OUTSIDE
SHORE,BEACH
OZ,WIZARD
DEODORIZE,STINK
HOW,TO
PROGRAM(E),CODE
REP,REPUTATION

The puzzle satisfies the series' inbuilt assumption, that each word can be tested for whether it is a Outside Word™ without relying on the other words.
These are not the only examples of Outside Words™; many more exist.

What is the special rule these words conform to?

 

 

Answer 1

I have a guess, though it doesn't seem to quite fit:

An Outside Word is one that consists only of letters from the outside columns of a standard phone keypad. That is, it has no letters out of {A,B,C,J,K,L,T,U,V}.

I'm fairly confident in this even though it doesn't quite fit:

It seems pretty clear to me that the Outside Words are restricted in what letters they can use. So what happens if we remove all of the letters appearing in an Outside Word from the entire list of words? We get this:


Most Non-Outside words have at least one letter left, except for a few: SQUASH, WAND, SESAME, PUZZLE, and WIZARD. I notice that A and U appear only once each on the left side, and could plausibly be an error; also, letters adjacent to them appear on the right side fairly often.

So, adding A and U back, we see that every Non-Outside word has at least one Outside-Unsafe letter.



So, assuming the two with a letter left are errors, it seems likely that an Outside Word is one that does not have an Outside-Unsafe Letter. These letters must include {A,U,C,T}, likely also include {B, K, V} (which appear in Non-Outside words, but not alone), and may or may not include {J, Y} (which do not appear in the entire puzzle).

Putting these sets together gives runs of letters that look suspiciously like the letters on a phone keypad.



And because of how nicely this lines up, and because of the title, I think it's safe to assume that L is also an error, and Outside Words are those that contain no letters from the middle column of a standard phone keypad.