1.  strengthening(n = noun.event) - becoming stronger;
is a kind of shift, transformation, transmutation
Antonym: weakening
Derived form verb strengthen₂

2.  strengthening(n = noun.act) - the act of increasing the strength of something;
is a kind of increase, step-up
has particulars: concentration
Antonym: weakening
Derived form verb strengthen₁

   That strengthens; giving or increasing strength. [1913 Webster]

N  strength, power, energy, vigor, force, main force, physical force, brute force, spring, elasticity, tone, tension, tonicity, stoutness, lustihood, stamina, nerve, muscle, sinew, thews and sinews, physique, pith, pithiness, virtility, vitality, athletics, athleticism, gymnastics, feats of strength, adamant, steel, iron, oak, heart of oak, iron grip, grit, bone, athlete, gymnast, acrobat, superman, Atlas, Hercules, Antaeus, Samson, Cyclops, Goliath, tower of strength, giant refreshed, strengthening, invigoration, refreshment, refocillation, dynamics, statics, strong, mighty, vigorous, forcible, hard, adamantine, stout, robust, sturdy, hardy, powerful, potent, puissant, valid, resistless, irresistible, invincible, proof against, impregnable, unconquerable, indomitable, dominating, inextinguishable, unquenchable, incontestable, more than a match for, overpowering, overwhelming, all powerful, all sufficient, sovereign, able-bodied, athletic, Herculean, Cyclopean, Atlantean, muscular, brawny, wiry, well-knit, broad-shouldered, sinewy, strapping, stalwart, gigantic, manly, man-like, manful, masculine, male, virile, unweakened, unallayed, unwithered, unshaken, unworn, unexhausted, in full force, in full swing, in the plenitude of power, stubborn, thick-ribbed, made of iron, deep-rooted, strong as a lion, strong as a horse, strong as an ox, strong as brandy, sound as a roach, in fine feather, in high feather, built like a brick shithouse, like a giant refreshed, strongly, by force, by main force, our withers are unwrung, Blut und Eisen, coelitus mihi vires, du fort au diable, en habiles gens, ex vi termini, flecti non frangi, he that wrestles with us strengthens our nerves an, inflexible in faith invincible in arms.