necessary evil

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

unnecessary

needlessness

行っていらっしゃい: alternative form of いってらっしゃい (itterasshai)

see you later (said by a person staying, a stock phrase required by the Japanese etiquette, lit.: (after) going, come back)

(humble) alternative form of いってきます (itte kimasu)

back and forth

(colloquial) Synonym of 行って来ます (itte kimasu, “see you later”)

to go and come back