思い切り
おもいきり · omoikiri · JLPT N2 · adverb
with all one's strength
思い切り = 思 (think) + 切 (cut): cut through hesitation and go all in
To act 思い切り is to cut off second thoughts and commit fully. Use it for all-out effort or for finally deciding to let go.
切 — 七 (phonetic) + 刀 (knife radical)
切 is a semantic-phonetic compound: 刀 'knife' gives the meaning of cutting, while 七 supplies the sound. The original sense was to slice or cut with a blade. From there it extended figuratively to 'close to' (as in pressed against) and 'urgent/earnest', as in 切实.