Symbolism, Imagery, Allegory
At one point in the story, Paul mistakenly hears his Uncle Oscar say "filthy lucker," instead of the idiomatic expression, "filthy lucre," which refers to money gained in a dishonorable way. (15-6)
Even though Paul misheard his uncle, his mistake seems to be a confusion that all the adult characters share. Everyone in the story, from wealthy Uncle Oscar to the humble gardener Bassett, associates luck with money and wealth. Starved for his mother's attention, Paul gets roped into this delusion too, and starts to associate money with earning his mother's love.
Of course, nobody seems to associate hard work and money, since both Paul's father and Bassett work but neither are wealthy. Paul makes a lot of money gambling, but at the cost of his physical and mental well-being. In "The Rocking-Horse Winner," money is the complete opposite of all that is human, including family affection and meaningful work.