The term 'DROP ACID' is a slang phrase that refers to the recreational use of the psychedelic drug LSD. The two crossword solutions, ETCH and TRIP, are both related to this phrase. ETCH is a verb meaning to carve or engrave a design into a hard surface, which is often used as a metaphor for the intense visual hallucinations experienced while under the influence of LSD. TRIP is another verb meaning to take a journey, usually referring to the intense mental journey experienced while on LSD.