|Origin:||solemne, from Latin solemnis 'ceremonial, formal, solemn'|
very serious and not happy, for example because something bad has happened or because you are at an important occasion:
a solemn expression
Their faces suddenly grew solemn.
a solemn procession of mourners
a solemn promise is one that is made very seriously and with no intention of breaking it:
I'll never be unfaithful again. I give you my solemn word.
performed in a very serious way