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

今春[konshun] this spring
昨春[sakushun] last spring
三春[sanshun] three spring months
思春期[shishunki] puberty
春たけなわ[harutakenawa] spring is in full swing

春めく[harumeku] to become spring-like
春一番[haruichiban] first storm of spring
春夏秋冬[shunkashuutou] spring, summer, autumn (fall) and winter
春画[shunga] shunga