fight / fīt/ • v. (past and past part. fought / fôt/ ) [intr.] take part in a violent struggle involving the exchange of physical blows or the use of weapons: the men were fighting. ∎  [tr.] engage in (a war or battle): ∎  [intr.] we fought and died for this country. ∎  quarrel or argue: they were fighting over who pays the bill. ∎  [tr.] struggle to put out (a fire, esp. a large one): two fire trucks raced to the scene to fight the blaze. ∎  [tr.] endeavor vigorously to win (an election or other contest). ∎  campaign determinedly for or against something, esp. to put right what one considers unfair or unjust: I will fight for more equitable laws. ∎  [tr.] struggle or campaign against (something): the best way to fight fascism abroad and racism at home. ∎  [tr.] attempt to repress (a feeling or an expression of a feeling): she had to fight back tears of frustration. ∎  [tr.] take part in a boxing match against (an opponent). ∎  (fight one's way) move forward with difficulty, esp. by pushing through a crowd or overcoming physical obstacles: she watched him fight his way across the room.• n. a violent confrontation or struggle. ∎  a boxing match. ∎  a battle or war: the country was not eager for a fight with the U.S. ∎  a vigorous struggle or campaign for or against something: a long fight against cancer. ∎  an argument or quarrel: she had a fight with her husband. ∎  the inclination or ability to fight or struggle: Ginny felt the fight trickle out of her.PHRASES: fight fire with fire use the weapons or tactics of one's enemy or opponent, even if one finds them distasteful.fight a losing battle be fated to fail in one's efforts: he was fighting a losing battle to stem the tears.fight or flight the instinctive physiological response to a threatening situation, which readies one either to resist forcibly or to run away.PHRASAL VERBS: fight back counterattack or retaliate in a fight, struggle, or contest.fight it out settle a dispute by fighting or competing aggressively: they fought it out with a tug-of-war.fight someone/something off defend oneself against an attack by someone or something: well-fed people are better able to fight off infectious disease.

fight fight fire with fire an injunction to counter like with like. The saying is recorded from the mid 19th century, but Shakespeare in Coriolanus (1608) has, ‘One fire drives out one fire, one nail one nail.’
fight or flight the instinctive physiological response to a threatening situation, which readies one either to resist forcibly or to run away.
he who fights and runs away, may live to fight another day an assertion of the value of knowing when to make a strategic withdrawal. A proverbial saying, mid 16th century; earlier in the writings of the Greek comic dramatist Menander (342–c.292 bc), ‘a man who flees will fight again.’ A Middle English variant is found in The Owl and the Nightingale (c.1250), ‘Wel fight that wel flight.’

see also that cock won't fight, fight one's corner, live to fight another day, fight tooth and nail.

fight pt., pp. fought do battle, contend. OE. str. vb. feohtan = OS., OHG. fehtan (Du. vechten, G. fechten) :- WGmc. *fχtan, formally identical with L. pectere comb.
So fight sb. OE. feohte wk. fem., (ġe)feoht str. n., corr. to OS., OHG. fehta, OHG. gifeht (Du. gevecht, G. gefecht).