The term OIL WELL fits nicely into the double-definition clueing style, the two meanings being -
1. (Noun) Underground shaft that produces oil
2. (Verb) Lubricate generously
This clue appeared in today's Guardian crossword No. 24514 (Araucaria), which made use of the double-definition.
Eliminate all friction from fuel source (3, 4) OIL WELL 
Another similar double-definition for this term appeared in ET Crossword No. 3570 last year.
Boring to make revolution much easier? (3,4) OIL WELL 
The last two clues use the same pun on the word BORING - the surface reading leads you to think of BORING(Verb)=dull, when the underlying definition is BORING(Noun)=drilled hole.