cố sức 
to endeavor, strive, make an effort, do one’s utmost [ cố ] : (1) to make an effort, try (very hard); (2) great grandfather; (3) to pawn; (4) reason; (5) old, former, late (deceased); (6) intentional, premeditated; (7) firm, strong; (8) innate, original; (9) to look after, care for, turn one’s head
[ sức ] : force, strength, might, power
Most Common Compounds Set 1:
Most Common Compounds Set 2 :