Problem: What are the most important words?
boaters relax waiting for lock to fill
Answer: boater, fill, lock, relax, wait

Problem: What are the most important words?
migrants wait to be rescued as they drift nautical miles north off the coast .
Answer: migrant, rescue, wait

Problem: What are the most important words?
an engraving entitled scanned at high resolution from a book published
Answer:
book, engrave, entitle, resolution, scan