"Card one sleeve" refers to keeping a card hidden up one's sleeve, often for the purpose of cheating in a game. Synonyms for this phrase may include phrases like "hidden card," "cheater's ace," "sleight of hand," or "deceitful tactic." Other phrases that may indicate this kind of behavior include "underhanded move," "shady business," or "unfair advantage." While games often involve strategy and competition, cheating is generally considered unethical and unsportsmanlike. It's important to participate in games with integrity and honesty, to maintain a sense of fairness and respect for other players.