strengthen

verb

1. (transitive)To make strong or stronger; to add strength to; to increase the strength of; to fortify.

   “strengthen a muscle”

   “strengthen a wall”

   “strengthen one's willpower”

   “strengthen one's authority”

   “Let noble Warwick, Cobham, and the rest,[…] With powerful policy strengthen themselves.”

2. (transitive)To empower; to give moral strength to; to encourage; to enhearten.

   “Charge Joshua, and encourage him, and strengthen him.”

   “my father and mother strengthened me in this my first impression, saying in my presence, I was intended for some great purpose”

   “"A fine man, that Dunwody, yonder," commented the young captain, as they parted, and as he turned to his prisoner. "We'll see him on in Washington some day. He is strengthening his forces now against Mr. Benton out there.[…]."”

   “A review of addiction research, published in Trends in Cognitive Sciences, suggests mindful meditation strengthens self-control in smokers, even among those smokers who haven’t set an intention to quit.”

3. (transitive)To augment; to improve; to intensify.
4. (transitive)To reinforce, to add to, to support (someone or something)

   “strengthen an army”

   “Each half-section of the battery weighs about eight tons, and the two underframes had to be strengthened to take this weight.”

   “In 2019, Trump signed the Fostering Undergraduate Talent by Unlocking Resources for Education (FUTURE) Act, a bipartisan bill aimed at strengthening HBCUs as well as other minority-serving institutions by providing $255 million annually.”

   “A priority for the new pope will be to strengthen the church’s unity amid differing views and expectations within the institution and growing polarisation in the wider world.”

5. (transitive)To substantiate; to corroborate (a belief, argument, etc.)

   “strengthen the cause”

6. (intransitive)To grow strong or stronger.

   “my affection seems so superfluous that I often wonder why it should be so strong. But wise or foolish, there it is, strengthening with the years whether I will or no”