make strong or stronger
"This exercise will strengthen your upper body"
"strengthen the relations between the two countries"
To make strong or stronger; to add strength to; to increase the strength of; to fortify.
"The new training program was designed to strengthen the team's defensive skills before the championship match."
In plain English: To strengthen means to make something stronger, more durable, or better able to handle stress.
"She worked out every day to strengthen her muscles."
Usage: Use strengthen when you want to indicate making something more robust, such as muscles through exercise or an argument with evidence. It is often confused with "fortify," but while both mean to make strong, strengthen applies broadly to abstract concepts like relationships and beliefs alongside physical objects.
The word "strengthen" likely originated from a reinterpretation of an earlier 12th-century verb, where speakers mistakenly analyzed it as meaning "to make strong." This form entered standard usage by the 14th century with that same core sense intact.