I am looking for a word or phrase regarding something that is "impossible". I can't seem to put my finger on it, but I am trying to think of the word to describe something that is the top of the top, and thus impossible to achieve? 

The only two words I have come up with are elusive and formidable, neither of which really mean what I want them to mean. I want something more clever to put it plainly.


Question: What does one do when one needs to bentch gomel?
Answer: As for women 'bentsching gomel', Dose of Halacha writes:


  ..The minhag is to recite it within 3 days of the incident after krias hatorah, though it may be recited later if necessary (Shulchan Aruch OC 219:6; Mishna Berura 20).
  
  The Chayei Adam (after 69) wrote a prayer after surviving an explosion. He writes that one should say this, along with the pesukim of the korban toda and give charity equal to the value of the animal he would have brought in Temple times. (See Mishna Berura 218:31).
  
  While women would also bring korbanei todah, the custom developed among many Ashkenazi communities that women don’t say the beracha, as the public recital is deemed immodest. The Magen Avraham (OC 219:4) writes that her husband should recite it on her behalf, while the Mishna Berura says that she recites it in front of ten women and a man. The Aruch Hashulchan (OC 219:6) suggests that this custom may have developed because women weren’t always present for Leining. Nonetheless, the Baer Hetev (219:1), Chayei Adam (65:6), Yechave Daas (4:15) and others all allow a woman to say it loudly from her side of the mechitza. Thus, Sefardi women should only say it in the presence of a minyan.
  
  In what is likely the last teshuva R’ Moshe Feinstein ever wrote (OC 5:14), he paskens that a new mother should recite the beracha in front of another, ideally her husband, and there is no need for a minyan.
  
  In England, we generally follow the Minchas Yitzchak (4:11). Women go to Shul and respond to their husband’s borchu and beracha (when he’s called up), with intent to thank Hashem.