A word puzzle which arose from the definition of arothelp: find words which when reversed (approximate reversal is acceptable) yield another word meaning the opposite thing.

Sylvar was the first to find a clever solution:

"madam" (a respectable lady) is the opposite of "madam" (a brothelkeeper)

A related variation would be to find words whose exact reversal yields an approximately opposite meaning. A very weak example which springs to mind is "evil--live". broken-winged bird also came up with:

There's "on," which is the electronic equivalent of "yes," but if you reverse it, spells "no."

Email me (or node) further suggestions.

Here's the complete list of reversible words from the /usr/dict/words file on Linux - I couldn't find any opposites.

• ah ha
• are era
• bag gab
• ban nab
• bard drab
• bat tab
• bats stab
• brag garb
• bud dub
• buns snub
• bus sub
• but tub
• dam mad
• decal laced
• deeps speed
• deer reed
• deliver reviled
• denier reined
• desserts stressed
• deus sued
• devil lived
• dial laid
• diaper repaid
• dim mid
• dog god
• don nod
• doom mood
• draw ward
• drawer reward
• edit tide
• eel lee
• em me
• emit time
• evil live
• fires serif
• flog golf
• flow wolf
• gas sag
• gel leg
• gnat tang
• gulp plug
• gum mug
• gums smug
• guns snug
• gut tug
• keel leek
• keels sleek
• keep peek
• knits stink
• lager regal
• lap pal
• leer reel
• leper repel
• lever revel
• liar rail
• loop pool
• loops spool
• loot tool
• loots stool
• meet teem
• mets stem
• nap pan
• naps span
• net ten
• nip pin
• nips spin
• no on
• not ton
• now won
• nuts stun
• pals slap
• pans snap
• par rap
• part trap
• parts strap
• pat tap
• paws swap
• peels sleep
• pets step
• pins snip
• pit tip
• pools sloop
• pot top
• pots stop
• rat tar
• rats star
• raw war
• redraw warder
• remit timer
• saw was
• snaps spans
• snoops spoons
• spat taps
• spit tips
• spot tops
• spots stops
• stew wets
• straw warts

---

Here's the quick and dirty source code I wrote. You can use it to try to find any in your native language. It's not very elegant, but it works. I didn't want to spend a lot of time on it. I spent more time making this node than writing it :)

Be sure to resize the MAX_WORDS define to be larger or equal to the number of words you will be sorting through.

#include <stdio.h>
#include <string.h>

#define MAX_WORDS 65536

char *words[MAX_WORDS];
char *revwords[MAX_WORDS];

void stripcrlf(char *s){
  int n;
  for(n=0;s[n];n++){
    if(s[n]==13 || s[n]==10){
      s[n]=0;
      break;
    }
  }
}

char *str_reverse(char *text){
  int g,t,n;
  char c;
  g=(t=strlen(text)-1)/2;
  for(n=0;n<=g;n++){
    c=text[n];
    text[n]=text[t-n];
    text[t-n]=c;
  }
  return text;
}

int main(){
  char text[4096];
  long numwords=0;
  int x,y;
  while(fgets(text,4096,stdin)){
    stripcrlf(text);
    if(text[0] && text[0] >= 'a' && text[0] <= 'z'){
      if(words[numwords]=strdup(text)){
        if(revwords[numwords]=strdup(text)){
          str_reverse(revwords[numwords]);
        }else{
          fprintf(stderr,"strdup error\n");
          exit(1);
        }
      }else{
        fprintf(stderr,"strdup error\n");
        exit(1);
      }
      numwords++;
    }
  }
  for(x=0;x<numwords;x++){
    for(y=x+1;y<numwords;y++){
      if(!strcmp(words[x],revwords[y])){
        printf("%s %s\n",words[x],words[y]);
      }
    }
  }
}

It's not an opposite but a reciprocal!

1 ohm (measure of resistance) = 1/mho (measure of conductance, also called a siemens)

Sorry, jafuser, I couln't resist rewriting your code as a perl one liner:

perl -ne 'chop;$w{reverse $_}=$_;print "$_\t$w{$_}\n" if $w{$_}'

Here is an unusual close-solution to the problem, taken from a book whose title was The Puzzling Adventures of Dr. Eco, I believe. (I was unable to verify the title or find the author, sadly).

If you take the word "up", and reverse it not by mirroring the letter-order, but by rotating it 180 degrees, you get "dn", the abbreviation for "down".

Two reversible words, with almost reverse meanings as well:

Amok (Amuck) vs. Coma

Depending on the spelling, these are literally reversible or not.