only one things

Those are words for only one thing. They are uncountable.
J.Font reading mean
一家 ikka a family; a household; one's family
一気 ikki at a [one] stretch [stroke]; at a breath
一興 ikkyou a fun
一見 ikken have [take] a look (at); glance (at)
一心 issin wholeheartedly; with one's whole heart; heart and soul; intently
一生 issyou one's life; a lifetime
一斉 issei all together; in unison; all at once; simultaneously; in chorus; unanimously; with one voice
一説 issetu according to one theory [authority, account]; one theory holds that…; someone says…; according to another view; to quote another authority
一体 ittai in a body; as one
一体化 ittaika integration
一旦 ittan once
一致 itti agreement; consistency; accord; coincidence
一定 ittei fixed; definite; regular; settled; specific; standard; a certain (amount of)
一派 ippa a school; a party; a faction; a sect
一筆 ippitu write a few lines or letter , write promise on paper
一命 itimei a life
一座 itiza a group of performers
一握り hitonigiri few people
一山 hitoyama a case, a success

TRANSLATION by Excite Dictionary / Italic word was added by me.