剛
ゴウ, かた, こう, ご, たか, たけ, たけし, つよ, つよし, ひさ, まさ, よし

sturdy, strength

JLPT1 G7 S10 F1576

As per 岡# (hard rope/cable) + 刀 sword/knife → cutting implement able to slice through a *strong* or *hard* object such as rope or cable.

[Full Kanji Etymology List]