A stroke of luck is a phrase used to describe an unexpected and fortunate event. The two crossword solutions for this term are 'FLUKE' (5 letters) and 'serif' (5 letters). A FLUKE is an event that happens by chance, while a serif is a type of font with small lines at the end of a letter's strokes. Together, these two words can be used to describe a stroke of luck, as it is an unexpected and fortunate event that happens by chance.