1. Luck is an uncountable noun referring to the concept of fortune, good fortune, or fortunate circumstances. The phrase "You never know your luck" suggests that one may unexpectedly encounter good fortune.2. Lucky is an adjective that describes something or someone as fortunate, opportune, or having achieved success through chance. The statement "He is a lucky dog" implies that the person in question has had a string of fortuitous events.3. Luckily is an adverb and is used to express the degree of fortunate circumstances or to indicate that something fortunate occurred. For example, "Luckily there was a doctor on the spot" indicates that it was fortunate that a doctor was present to assist.