The term 'dirty trick' can be defined as a deceptive or underhanded action intended to gain an advantage. The crossword solutions for this term are SMEAR (5 letters), RUSE (4 letters), GUILE (5 letters), FASTONE (7 letters), SLYNESS (7 letters), and MISCHIEF (8 letters). SMEAR is an attempt to damage someone's reputation by spreading false information. A RUSE is a clever trick used to deceive someone. GUILE is a cunning or crafty intelligence. A FASTONE is a clever trick or joke played on someone. SLYNESS is the quality of being sly or cunning. Lastly, MISCHIEF is behavior that causes trouble or damage.