勢い
いきおい
force
vigor
energy
spirit
life
authority
influence
power
might
impetus
course (of events)
tendency
necessarily
勢いを振るう
いきおいをふるう
to wield power
to exercise authority
勢い付く
いきおいづく
to gather strength
to take heart
勢い良く
いきおいよく
vigorously
勢い込む
いきおいこむ
to brace oneself