(adj): characterized by a firm and humorless belief in the validity of your opinions
(adj): dignified and somber in manner or character and committed to keeping promises
(adj): excessively serious
(adj): not to be taken lightly
(adj): acting with or showing thought and good sense
(adj): tending to make sober or more serious
(adj): of a substantial character and not frivolous or superficial
(adj): of great consequence
(adj): vs. unimportant), of import -- (of great significance or value
(adj): causing fear or anxiety by threatening great harm
(adj): vs. noncritical) -- (being in or verging on a state of crisis or emergency
(adj): appealing to the mind
(adj): vs. nonintellectual) -- (appealing to or using the intellect
(adj): vs. playful), serious, sober -- (completely lacking in playfulness
(adj): requiring effort or concentration; complex and not easy to answer or solve
(adj): vs. easy), hard -- (not easy; requiring great physical or mental effort to accomplish or comprehend or endure