lud/lus

play, mock

Spelled lud, lus · ludere 'play, mock,' with participial stem lus-; ludus 'play, game'

Latin ludere meant play: to allude was to play toward something; delude and collusion turned play into deception.

Words built from it

ludicrous — so absurd that it seems ridiculous
lud (play) + -icrous (relating to)
allude — refer to something indirectly
al- (toward; form of ad-) + lud (play)
delude — make someone believe something false
de- (intensive) + lud (mock)
elude — escape or avoid being caught or understood
e- (away; form of ex-) + lud (play)
illusion — a misleading appearance or false belief
il- (against; form of in-) + lus (mock) + -ion (action or result)
collusion — secret cooperation intended to deceive
col- (together; form of com-) + lus (play) + -ion (action or result)

lustrous — Contains lus, but comes from luster, meaning brightness, rather than ludere, meaning play.