1.NounSomething with ongoing consequences; usually, one with positive ongoing consequences.
"Those flower bulbs that our neighbor gave us are a gift that keeps on giving — they keep blooming year after year.; That one-night stand that some tramp gave him is a gift that keeps on giving — he's had syphilis for years now."
2.NounA sexually transmitted disease.
"That one-night stand that some tramp gave him is a gift that keeps on giving — he's had syphilis for years now."