kerdainō

The picture behind this word is the marketplace. A merchant puts capital to work and comes away with more than was put in, and that return is what this verb names. Its everyday range covers turning a profit and acquiring possessions, up to the sweeping figure of gaining "the whole world" (only to be warned that the trade is worthless if it costs one's own soul).

The New Testament then stretches the same image in a striking direction. To bring a person to faith, or to win an estranged fellow believer back, is described with this very verb: the person won is spoken of as the gain, the profit that the effort brings in. So Paul can say he made himself the servant of all in order to "win" as many as possible, and to win a brother who has sinned is to gain him (κέρδος is the matching noun for the profit itself).

What holds the senses together is that in each one someone ends up richer for the effort, whether the increase is money, a possession, or a human being brought in. The English words shift ("gain," "make a profit," "win"), but the Greek keeps one verb across them all.

In one place the verb runs in reverse. Paul tells the crew of the doomed ship that they should have listened to him and so "gained" the injury and loss, which is an ironic, turned-around way of saying they would have spared themselves the damage. The word for making a profit is used for the profit that consists of a loss never taken: the best return here is the harm you manage to avoid.

This is a recognized twist on the ordinary sense rather than a separate word. English cannot keep the pun, so translators simply render it "spared" or "avoided."