slacker (Adjective) — Not tense or taut. ex. "slack and wrinkled skin" ex. "slack sails" ex. "a slack rope"
slacker (Adjective) — Flowing with little speed as e.g. at the turning of the tide. ex. "slack water"
slacker (Adjective) — Lacking in rigour or strictness. ex. "slack in maintaining discipline"
slacker (Noun) — (military) a person who shirks his work or duty (especially one who tries to evade military service in wartime).
slacker (Noun) — A lazy person.