dict.m

#import <Cocoa/Cocoa.h>
#import <CoreServices/CoreServices.h>

int main(int argc, char *argv[])
{
  NSString *word;
  NSString *result;

  if (argc > 1) {
    word = [[NSString alloc] initWithUTF8String:argv[1]];
    result = (NSString *)DCSCopyTextDefinition(NULL, (CFStringRef)word, CFRangeMake(0, [word length]));
    // NSLog(@"word: %@", word);
    // NSLog(@"result: %@", result);
    if (result) {
      printf("%s", [result UTF8String]);
      return 0;
    }
  }
  return 1;
}

Makefile

all:
	gcc -o dict -Wall -fobjc-gc -O2 -std=c99 dict.m -framework carbon -framework cocoa