Lack means not having enough of something you need or want, or having none of it at all. When there's a lack of rain during summer, gardens dry up and plants struggle. When a team shows a lack of practice, their skills aren't sharp enough to compete well.

The word works as both a noun and a verb. You might say “The project suffered from a lack of planning” (noun), or “The old computer lacks enough memory to run new programs” (verb). Notice how lack implies something missing that should be there, something whose absence creates a problem.

Lack is different from simply not having something. You don't have a rocket ship, but you don't lack one because you don't need it. You lack something when its absence matters: a plant lacks water, a story lacks excitement, or a solution lacks creativity.

The word lacking describes something incomplete or inadequate. A lacking explanation leaves questions unanswered. When someone says “Your argument is lacking,” they mean it's not strong or complete enough to be convincing.