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
Latin ludus (play) → ludicrus (playful) → ludicrous
allude — refer to something indirectly
ad- (toward) + ludere (play) → alludere (play toward, refer to)
delude — make someone believe something false
de- (intensive) + ludere (play, mock) → deludere (deceive)
elude — escape or avoid being caught or understood
ex- (out, away) + ludere (play) → eludere (evade, escape)
illusion — a misleading appearance or false belief
in- (against) + ludere (mock) → illudere (deceive) → illusio (deception)
collusion — secret cooperation intended to deceive
com- (together) + ludere (play) → colludere (play together, conspire) → collusio

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