verb

• (intransitive) To writhe with agony; to suffer violent anguish.
  "His Touch, if tremblingly alive all o’er, / To smart, and agonize at ev’ry pore?"
• (intransitive) To struggle; to wrestle; to strive desperately, whether mentally or physically.
  "So I took a last stare round, agonizing to see if there was any way of escape; but the stone walls and roof were solid enough to crush me, and the stack of casks too closely packed to hide more than a rat."
• (transitive) To cause agony or anguish in someone.
  "That dreadful bill […] was one of the chief torments of her life. At all hours of the night or day it was waiting just round the corner of her consciousness, ready to spring upon her and agonise her […]"
• (transitive, biochemistry, pharmacology) To act as an agonist upon; to combine with a receptor on a cell to produce a physiological reaction.