Объединение в одну коллекцию

gistfile1.txt

using System;
using System.Collections.Generic;

namespace Task003
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string[] words1 = new string[] {"привет", "пока", "собака", "кошка", "привет"};
            string[] words2 = new string[] {"кошка", "лошадь", "корова", "пока"};
            List<string> allWords = new List<string>();

            AddInList(allWords, words1);
            AddInList(allWords, words2);

            PrintList(allWords);
        }

        static void AddInList(List<string> allNumbers, string[] numbers)
        {
            for (int i = 0; i < numbers.Length; i++)
            {
                if (allNumbers.Contains(numbers[i]) == false)
                {
                    allNumbers.Add(numbers[i]);
                }
            }
        }

        static void PrintList(List<string> words)
        {
            foreach (string word in words)
            {
                Console.Write(word + " ");
            }
        }
    }
}