Synonyms: boring, monotonous, tedious, irksome, tiresome
These adjectives refer to what is so lacking in interest as to cause mental weariness. Something that is boring fails to hold one's interest or attention, often resulting in listlessness or impatience: I had never read such a boring book.
What is monotonous bores because of lack of variety: "There is nothing so desperately monotonous as the sea" (James Russell Lowell).
Tedious suggests dull slowness, long-windedness, or stultifying routine: "It was a life full of the tedious, repetitive tasks essential to small-press publishing and grassroots organizing" (Jan Clausen).
Irksome emphasizes the irritation or resentment provoked by something tedious: "I know and feel what an irksome task the writing of long letters is" (Edmund Burke).
Something tiresome fatigues because it seems to be interminable or to be marked by unremitting sameness: "What a tiresome being is a man who is fond of talking" (Benjamin Jowett).