(university slang) During the attendance check, deceiving a lecturer into thinking another person is in attendance by answering for them.

(university slang) During the attendance check, to deceive a lecturer into thinking another person is in attendance by answering for them.

(formal, literally or figuratively) dirtiness

(formal, literally or figuratively) to be dirty

(obsolete, military) battery

necessity (quality or state of being necessary, unavoidable, or absolutely requisite)

unnecessary

needlessness

necessary evil

The hiragana syllable ぼ (bo). Its equivalent in katakana is ボ (bo).