Ask them for X number words of six letters or more which contain NO vowels: I'll start you off with syzygy, much loved by my father.
Are you doing themes? If you get a theme of 'weapons' going, you could ask what a yataghan is. It's a C19 Turkish sword with a curved blade.
Animal themes: 1. What is a yapok? It's an amphibious nocturnal opossum of Central and S. America, aka the water opossum. 2. As bovine is to cow, what is ursine, and vulpine? (Bear, and fox.) 3. How do you spell the name 'vizsla', which is a breed of Hungarian hunting dog? (Pro. vizzla)
Spelling: 1. How many 'rs' in 'underrated'? 2. How many 'es' in 'topsy-turvy'? 3. Spell 'reminiscent'.
Sport: 1. In which game would you find a tambour? (Real tennis. It's the sloping buttress on one side of the receiver's end of the court.) 2. How many red balls in a game of snooker? (15.) 3. If a horse race is 16 furlongs, what is the nearest distance in meters? (3200m.)
Fashion: 1. What was the colour associated with the Italian fashion designer Elsa Schiaparelli? (Shocking pink.) 2. What was the name of the streamlined style designed by Christian Dior after WWII? (New Look.) 3. What is the number given to Coco Chanel's most famous perfume? (Chanel No.5) 4. Who developed the popular chain of boutiques known as 'Biba' in the 1960s? (Barbara Hulanicki.)
Weapons: Which of these weapons were named after their inventors: shrapnel, grenade, howitzer, mortar, and torpedo? (Only shrapnel.)
Trees: What are these: Totara, gingko, acer, and jacaranda?
Further ideas upon request. Please send ssae.