Lack/læk/ Definition 1 of 3Pro Tip 1/3Not Enough Use 'lack' to stress insufficiency that affects outcomes, like projects or plans. The failure was attributed to a lack of planning. Pro Tip 2/3Express Concern 'Lack of' often implies a problem that should be addressed or is regrettable. There's a disturbing lack of transparency in the process. Pro Tip 3/3Common Pairings 'Lack of' frequently pairs with abstract nouns like 'interest', 'knowledge', or 'evidence'. Her lack of interest in the subject was evident.