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

安全期[anzenki] safe period
暗黒期[ankokuki] eclipse period
一期[ichigo] one's life time
一期[ikki] one term
一期一会[ichigoichie] once-in-a-lifetime encounter (hence should be cherished as such)

一周期[isshuuki] period (in astronomy)
一定期間[itteikikan] fixed interval
延期[enki] postponement
延期になる[enkininaru] to be postponed
沖積期[chuusekiki] alluvial period

亜鉛末[aenmatsu] zinc dust
学期末[gakkimatsu] end of term
巻末[kanmatsu] end of a book
期末[kimatsu] end of term
期末試験[kimatsushiken] final exam

旧年末[kyuunenmatsu] end of last year
結末[ketsumatsu] end
月末[getsumatsu] end of the month
跡始末[atoshimatsu] settlement (of affairs)
語末[gomatsu] end of a word