Sentence:  Mercer 's Whiteman association brought him into contact with Hoagy Carmichael , whose `` Snowball '' Mercer relyriced as `` Lazybones '' , in which form it became a hit and marked the real <WSD>beginning</WSD> of Mercer 's song writing career . 
Meaning of the word marked with <WSD> tags:  the event consisting of the start of something