Sentence:  The term, "<WSD>head</WSD>," is, of course, not new with hippies. It has a long history among drug users generally, for whom it signified a regular, experienced user of any illegal drug—e.g., pot "head," meth "head," smack (heroin) "head." 
Meaning of the word marked with <WSD> tags:  A heavy or habitual user of illicit drugs.