pattern - What is a Regular Word™?

If a word has a certain property, I call it a Regular Word™.

You can use the examples below to find the property:

$$\begin{array}{|c|c|} \hline \bbox[yellow]{\textbf{Regular Words™}}&\bbox[yellow]{\textbf{Not Regular Words™}}\\ \hline \text{NAP}&\text{SLEEP}\\ \hline \text{AXED}&\text{FIRED}\\ \hline \text{QUIT}&\text{EXIT}\\ \hline \text{WHIZ}&\text{GENIUS}\\ \hline \text{DEATH}&\text{EXPIRY}\\ \hline \text{GREEK}&\text{LATIN}\\ \hline \text{BOXING}&\text{FIGHTING}\\ \hline \text{KIDNAP}&\text{ABDUCT}\\ \hline \text{OBJECT}&\text{THING}\\ \hline \text{REVIEW}&\text{PERUSE}\\ \hline \text{SPHINX}&\text{RIDDLER}\\ \hline \text{HEXAGON}&\text{PENTAGON}\\ \hline \text{MOSQUES}&\text{TEMPLES}\\ \hline \text{FEMINISM}&\text{EQUALITY}\\ \hline \text{LUXURIANT}&\text{LAVISH}\\ \hline \text{CONTEXTUAL}&\text{RELATED}\\ \hline \text{EXCAVATION}&\text{DIGGING}\\ \hline \text{JUXTAPOSES}&\text{OVERLAPS}\\ \hline \text{PERPLEXITY}&\text{CONFUSION}\\ \hline \text{INTOXICATES}&\text{INEBRIATES}\\ \hline \end{array} $$

For those without MathJax, or if you want to pop this into a spreadsheet, here is a CSV version:

Regular™,Not Regular™
NAP,SLEEP
AXED,FIRED
QUIT,EXIT

WHIZ,GENIUS
DEATH,EXPIRY
GREEK,LATIN
BOXING,FIGHTING
KIDNAP,ABDUCT
OBJECT,THING
REVIEW,PERUSE
SPHINX,RIDDLER
HEXAGON,PENTAGON
MOSQUES,TEMPLES

FEMINISM,EQUALITY
LUXURIANT,LAVISH
CONTEXTUAL,RELATED
EXCAVATION,DIGGING
JUXTAPOSES,OVERLAPS
PERPLEXITY,CONFUSION
INTOXICATES,INEBRIATES

Answer

A Regular Word™ is a word in which

The length of the word is the same as the distance between the first and last letters in the alphabet.

In other words, the number of letters between the first and last letters of the word is also the number of letters between them in the alphabet.

for example

"MOSQUES" has the same number of letters as "MNOPQRS," and "EXCAVATION" has the same number of letters as "EFGHIJKLMN"