Like some oaths (6)
I believe the answer is:
solemn
'like some oaths' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for solemn that I've seen before include "Grave and serious about melons" , "Serious and humourless" , "'Sedate, grave (6)'" , "'Dignified, sombre (6)'" , "'Earnest, grave (6)'" .)