夏季休暇[kakikyuuka] summer vacation
季刊[kikan] quarterly (e.g. magazine)
季語[kigo] seasonal word (in haiku)
季候[kikou] season
季節[kisetsu] season

季節はずれ[kisetsuhazure] unseasonable
季節的[kisetsuteki] seasonal
季節風[kisetsufuu] seasonal winds
四季[shiki] four seasons
冬季[touki] (season of) winter

隈無く[kumanaku] all over
然り気無い[sarigenai] nonchalant
だらし無い[darashinai] slovenly
途轍も無い[totetsumonai] extravagant
とんでも無い[tondemonai] unthinkable

無け無し[nakenashi] very small amount which looks like nothing
無駄にする[mudanisuru] to render futile
悪虐無道[akugyakubudou] treacherous
意気地無し[ikujinashi] coward
一も二も無く[ichimonimonaku] unhesitatingly