Definition of "strengthen"

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

c. 1596–1599 (date written), William Shakespeare, “The Second Part of Henry the Fourth, […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, (please specify the act number in uppercase Roman numerals, and the scene number in lowercase Roman numerals)

A little hardship, and a little struggling with the rougher elements of life, will perchance but strengthen and increase his courage, and prepare him for the conflicts and struggles of after years.

1851, anonymous author, Arthur Hamilton, and His Dog‎

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

1831, Nat Turner, The Confessions of Nat Turner

Charge Joshua, and encourage him, and strengthen him.

1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], Deuteronomy iii:28

"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. […]."

1910, Emerson Hough, chapter I, in The Purchase Price: Or The Cause of Compromise, Indianapolis, Ind.: The Bobbs-Merrill Company

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

1914, Elizabeth Robins Pennell, Our Philadelphia