# What is a Reciprocal 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.

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

$$\begin{array}{|c|c|}\hline \bbox[yellow]{\textbf{Reciprocal Words }^™}& \bbox[yellow]{\textbf{Not Reciprocal Words }^™}\\ \hline \text{ COMMENT }&\text{ REPLY }\\ \hline \text{ PULP }&\text{ FICTION }\\ \hline \text{ FOOL }&\text{ JOKER }\\ \hline \text{ STARTS }&\text{ BEGINS }\\ \hline \text{ REGGAE }&\text{ DANCEHALL }\\ \hline \text{ FLUID }&\text{ SOLID }\\ \hline \text{ INTERNAL }&\text{ EXTERNAL }\\ \hline \text{ RESEARCHER }&\text{ INVESTIGATOR }\\ \hline \text{ OUZO }&\text{ SAMBUCA }\\ \hline \text{ POSTMAN }&\text{ TAMPONS }\\ \hline \text{ ACHING }&\text{ HURTING }\\ \hline \text{ TEST }&\text{ DRIVE }\\ \hline \text{ PECAN }&\text{ WALNUT }\\ \hline \text{ INTEND }&\text{ AIM }\\ \hline \text{ WRECKING }&\text{ BASHING }\\ \hline \text{ FAMINE }&\text{ HUNGER }\\ \hline \text{ SCALE }&\text{ MODEL }\\ \hline \end{array}$$

In case you want it in CSV:

Reciprocal Words™,Not Reciprocal Words™
PULP,FICTION
FOOL,JOKER
STARTS,BEGINS
REGGAE,DANCEHALL
FLUID,SOLID
INTERNAL,EXTERNAL
RESEARCHER,INVESTIGATOR
OUZO,SAMBUCA
POSTMAN,TAMPONS
ACHING,HURTING
TEST,DRIVE
PECAN,WALNUT
INTEND,AIM
WRECKING,BASHING
FAMINE,HUNGER
SCALE,MODEL


The puzzle relies on the series' inbuilt assumption, that each word can be tested for whether it is a Reciprocal Word™ without relying on the other words.

These are not the only examples of Reciprocal Words™, many more exist.

Hint:

You'd better not suffer from aibohphobia if you want to solve this puzzle.

• It is about a pattern, yes? No anagrams involved? Because the only approximation to an answer I got thus far is encroaching on anagram. – Weckar E. Nov 17 '16 at 9:17
• No anagrams involved. Just focus on the hint I gave. Although, maybe not in the regular way... – Levieux Nov 17 '16 at 9:24

A Reciprocal Word™ is one that

When written in morse code is a palidrome.

Example

RESEARCHER in morse code is $.-.......-.-.-.-.......-.$ which reads the same backwards and forwards.

Other examples

COMMENT = $-.-.-------.-.-$
PULP is $.--...-.-...--.$
FOOL is $..-.------.-..$
STARTS is $...-.-.-.-...$
REGGAE is $.-..--.--..-.$
FLUID is $..-..-....-..-..$
INTERNAL is $..-.-..-.-..-.-..$

The are called Reciprocal because

When translated to morse, the word is its own reciprocal, i.e, a palindrome.

EDIT: This guess has been proven wrong.

The best I can figure, a Reciprocal Word is one which

Contains a least one word within itself (can use the first or last letter but not both obviously), either backwards or forwards, and does not lose this property if the first and last letters are swapped.

First word:

comMENt

Second word:

PUlp (up is backwards)

The rest:

Fool (loo, of), starts (star and arts), reggae (egg), fluid (flu,if), internal (an, backwards), researcher (search), ouzo (ou), postman (post,man,no,map), aching (chin), test (set, backwards), pecan (ace, backwards), intend (ten), wrecking (kin), famine (in), scale (ale,ace)

• Why is Walnut not a reciprocal then? – VHS Nov 16 '16 at 16:47
• Good point. I didn't go through all the non reciprocals and compare them. Looks like I'm still missing something then. My guess is the only pattern I could come up with. – Tim Nov 16 '16 at 17:01
• Nope, that's not it. I'll add a little hint in a minute. – Levieux Nov 17 '16 at 7:48
• Also there is the word "ode" in model – Oreo Nov 17 '16 at 9:01
• Begins (Gin) / Dancehall (Dance, Lance) / External (Tern) / Investigator (Vest) / Drive (Rive, Ire) / Sambuca (Cub) / Tampons (Amp) / Hurting (Tin) / Bashing (Shin) / Hunger (Hung, Rung) / Model (Ode) are all non-reciprocal but fit your pattern – Joe Nov 17 '16 at 9:04