須 - ought, by all means, necessarily

indispensable; essential; requisite; required; compulsory; necessary

essential condition

indispensable case

single-stringed Japanese zither

mackerel tuna (Euthynnus affinis); little tuna; kawakawa

spout of a teapot

blue whale (Balaenoptera musculus)

beard

unsun karuta; Japanese deck of cards with 5 suits of 15 cards each

ridged whale meat used to make whale "bacon"

mandatory attribute; required attribute

required entry (e.g. in online forms)