• 虚むなしい — empty; meaningless; in vain
• 虚偽きょぎ — falsehood; lie
• 虚構きょこう — fiction; something fabricated
• 虚勢きょせい — bluff; putting on a brave front
• 虚弱きょじゃく — weakness; fragility
• 虚言きょげん — false talk; lying
• 虚飾きょしょく — ostentation; showy display; putting on airs
• 虚数きょすう — imaginary number (math term)

虚 is a phono-semantic character. The top part 虍 is the “tiger” radical, and the lower part provides the sound for キョ. In modern Japanese it no longer means “tiger,” but keeps the idea of something impressive on the outside and hollow on the inside — empty form without real substance.