lac / lack are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
lac: (noun) resinlike substance secreted by certain lac insects; used in e.g. varnishes and sealing wax.
lack: (noun) the state of needing something that is absent or unavailable.
lac: l·AE·k
lack: l·AE·k
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)