Adjective

Felt or believed deeply and sincerely.

She expressed her heartfelt sympathies at the death of his mother.

Adjective

(er)

Capable of producing great physical force.

Capable of withstanding great physical force.

fast moving water, wind, etc, which has a lot of power.

Determined; unyielding.

* , chapter=10

, title= The Mirror and the Lamp , passage=It was a joy to snatch some brief respite, and find himself in the rectory drawing–room. Listening here was as pleasant as talking; just to watch was pleasant. The young priests who lived here wore cassocks and birettas; their faces were fine and mild, yet really strong , like the rector's face; and in their intercourse with him and his wife they seemed to be brothers.}}

Highly stimulating to the senses.

Having an offensive or intense odor or flavor.

Having a high concentration of an essential or active ingredient.

(specifically) Having a high alcoholic content.

(grammar) Inflecting in a different manner than the one called weak, such as Germanic verbs which change vowels.

(military) Not easily subdued or taken.

(slang, US) Impressive, good.

Having a specified number of people or units.

(of a disease or symptom) (l) (very bad or intense)

* 2005 , Andrew Gaeddert, Healing Immune Disorders: Natural Defense-Building Solutions , North Atlantic Books, page 221:

Physicians may diagnosis influenza by a throat culture or blood test, which may be important if you have a particularly strong flu, if your doctor suspects pneumonia or a bacterial infection.

(mathematics, logic) Having a wide range of logical consequences; widely applicable. (Often contrasted with a statement which it implies.)