with all one's might; to one's heart's content; as much as possible; really hard
Everyday adverb meaning to do something fully, without holding back: as hard as one can, as much as one wants, or very strongly. It can also intensify a negative or accidental action, like hitting something really hard.
See also: 思い切り
久しぶりに海で思いっきり泳いだ。
I swam in the sea to my heart's content for the first time in ages.
Run as hard as you can until the end.
I hit my head really hard on the door.
resolve; decisiveness; determination; resignation
Noun use is much less common than the adverb and appears mainly in fixed expressions such as 思いっきりがいい or 思いっきりがつかない. For more standard writing, 思い切り is often preferred.
See also: 思い切り
He was decisive and quit the company without hesitation.
I could not bring myself to sell the old house.
I swam in the sea as hard as I could.
On my day off, I enjoyed myself to the fullest.
I ended up crying my heart out watching the movie.
The bicycle crashed hard into the utility pole.
He's decisive, so even after a failure he quickly moves on.
I want to throw out the old furniture, but I can't bring myself to decide.