Twice in the O.T. a mysterious question is put to humans when they enquire as to the name of what appears to them to be an angel or a divine one. The first is Jacob, who is renamed Israel after wrestling all night and having his hip disjointed by this one. Jacob asks for this one's name only to be asked the question (Genesis 32:29):
Why [is] this, thou asketh for my name? - YLT
Wherefore is it that thou dost ask after my name? - AV
Why do you ask my name? - NIV
Why do you want to know my name? - GNB
Then, when Manoah asks an angel for his name, similarly he also is asked a question (Judges 13:18):
Why is this - thou dost ask for my name? - and it is Wonderful. - YLT
Why asketh thou after my name, seeing it is secret? - AV
Why do you ask my name? It is beyond understanding. - NIV
Why do you want to know my name? It is a name of wonder. - GNB
The Hebrew word that is variously translated 'wonderful' or 'secret' seems to be pele, or pili, and only occurs in Judges 13:18 (according to Young's Concordance page 848).
Can it mean both 'wonderful' and 'secret'?
Is it too wonderful a name to speak to mortals - and why would that be?
Is it too secret to be known by humans - and why would that be?