勢 （セイ） strength, power, energy, military strength, army, (number of) troops

勢力 （セイリョク） influence, power, might, strength, potency, force, energy

国勢 （コクセイ） state of a country (population, resources, etc.), condition of a country, strength of a country

党勢 （トウセイ） strength of a party

勢 （ゼイ） group (of people, players, companies, etc.), camp, team

同勢 （ドウゼイ） party, company

猛勢 （モウセイ） great strength, courageous army, valiant troops

勢い （いきおい） force, vigor, vigour, energy, spirit, life, influence, authority, power, might, impetus, momentum, course (of events), naturally, necessarily

勢い余る （いきおいあまる） to have excess momentum (from going too fast, using too much force, etc.), to get carried away, to go overboard, to overdo (something)

弾み （はずみ） bounce, spring, rebound, momentum, impetus, impulse, stimulus, inertia, moment, instant, impulse, chance

弾車 （はずみぐるま） flywheel