(drama, film) a song sung between acts or similar breaks; an intermezzo / (anime) insert song; a piece of incidental music

quack doctor

necessary evil

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

unnecessary

needlessness

having a comeback or excuse for everything one is told, being smart in the sense of having a smart mouth

hard to say, inexpressible, hesitant to say

Alternative form of 言うは易く行うは難し

to express well, to be articulate