Discount is a safest word I think.Does the word "discount" or bonus or reward is red flag for Google ?
Have you overseen an article or parasite ranks on Google top 30 with this word in title ?
Is that so? so do you think you can game the system that way?If you are a huge established brand you can write ''pussy" on the title and it will rank without consequences
If you are a micro website or small brand, maybe ''discount" could be a word to reconsider