Final answer:
The word defined as 'dull; somber; serious' is likely 'solemn.'
Step-by-step explanation:
The term you are looking for that is defined as dull; somber; serious is likely to be 'solemn.' When looking up words to understand their meanings in a dictionary, it's important to remember the context in which you encountered the word as that can affect its meaning. For instance, one might say, 'The mood at the memorial service was solemn, with everyone reflecting on the gravity of the loss.'