The word "Humdrum" is the correctly spelled word among the options provided. It refers to something that is dull, routine, or lacking variety.
- (1) "Hlalaballoo" is misspelled, the correct word is "Hullabaloo."
- (2) "Hypeteneuse" is misspelled, the correct word is "Hypotenuse."
- (4) "Humourus" is misspelled, the correct word is "Humorous."
Thus, the correct answer is (3) Humdrum.