pattern - What is an Unlucky Word™?

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

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If a word conforms to a special rule, I call it an Unlucky Word™.
Use the examples below to find the rule.

$$ % set Title text. (spaces around the text ARE important; do not remove.) % increase Pad value only if your entries are longer than the title bar. % \def\Pad{\P{0.0}} \def\Title{\textbf{ Unlucky }} % \def\S#1#2{\Space{#1}{20px}{#2px}}\def\P#1{\V{#1em}}\def\V#1{\S{#1}{9}} \def\T{\Title\textbf{Words}^{\;\!™}\Pad}\def\NT{\Pad\textbf{Not}\T\ }\displaystyle \smash{\lower{29px}\bbox[green]{\phantom{\rlap{rubio.2019.05.15}\S{6px}{0} \begin{array}{cc}\Pad\T&\NT\\\end{array}}}}\atop\def\V#1{\S{#1}{5}} \begin{array}{|c|c|}\hline\Pad\T&\NT\\\hline % \text{ GREEN }&\text{ JADE }\\ \hline \text{ RAIL }&\text{ TRAIN }\\ \hline \text{ FUR }&\text{ WOOL }\\ \hline \text{ VEX }&\text{ ANNOY }\\ \hline \text{ ONYX }&\text{ BLACK }\\ \hline \text{ FLAP }&\text{ WAVE }\\ \hline \text{ SYNC }&\text{ DATA }\\ \hline \text{ ONE }&\text{ UNIT }\\ \hline \text{ BALK }&\text{ RESIST }\\ \hline \text{ ART }&\text{ NICE }\\ \hline \text{ ENVY }&\text{ SPITE }\\ \hline \text{ ROOF }&\text{ FLOOR }\\ \hline \text{ NOWHERE* }&\text{ SILENCE }\\ \hline \end{array}$$                                         * This is an Unluckiest Word™

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

Unlucky Words™,Not Unlucky Words™
GREEN,JADE
RAIL,TRAIN
FUR,WOOL

VEX,ANNOY
ONYX,BLACK
FLAP,WAVE
SYNC,DATA
ONE,UNIT
BALK,RESIST
ART,NICE
ENVY,SPITE
ROOF,FLOOR
NOWHERE,SILENCE

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

What is the special rule these words conform to?
Why are they called Unlucky and Unluckiest Words™?

Good luck!

Answer

Unlucky Words™ are ones which

When rot13 translated, produce another word.

The below shows the words

with the rot13 cipher applied:

ENVY,GENVA
SHE,JBBY
IRK,NAABL
BALK,OYNPX
SYNC,JNIR
FLAP,QNGN
BAR,HAVG

ONYX,ERFVFG
NEG,AVPR
RAIL,FCVGR
EBBS,SYBBE
ABJURER,FVYRAPR

They are called this as 13 is often considered unlucky, and the longest word of this type is abjurer.