This puzzle is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles.
If a word conforms to a special rule, I call it a range word. Here is a list of range and not-range words:
+-----------+-----------+
| RANGE | NOT RANGE |
+-----------+-----------+
| orb | circle |
| banjo | guitar |
| bamboo | wood |
| ear | mouth |
| easier | harder |
| megahertz | gigahertz |
| haiku | sudoku |
| Hindu | temple |
+-----------+-----------+
And CSV version:
RANGE,NOT RANGE
orb,circle
banjo,guitar
bamboo,wood
ear,mouth
easier,harder
megahertz,gigahertz
haiku,sudoku
Hindu,temple
QUESTION: What is the rule to tell whether a word is a range word or not?