Do you think you have developed a fear of this word or are very conscious when you have to say this? Often when we stutter on a particular word once or twice our brain tricks into making us believe that word is difficult for us. You can try and exaggerate this word when you are saying it in conversations or slow down when this word comes up. Also, remind yourself that no word is difficult for you. If you can say other words so fluently then, of course, you can say this too.