可し - JP-EN Jisho

可(べ)し

auxiliary'ku' adjective (archaic)formal or literary termword usually written using kana alone

must; should; ought to

See also:

auxiliary adjective'ku' adjective (archaic)formal or literary termword usually written using kana alone

will (surely); be bound to; must

auxiliary'ku' adjective (archaic)formal or literary termword usually written using kana alone

will (do); shall

indicates volition