一期一会 is a meeting that will not come again. In the tea room, host and guest give one gathering their whole attention for that reason. The word has grown past tea to any meeting, and our title, Each Moment Only Once, follows that wider sense. The dictionaries carry both senses, and which one you take is yours.
The four-character word 一期一会 is first known from the preface to Ii Naosuke 井伊直弼's tea manual 茶湯一会集, drafted in the 1840s and finished in 1858, which says the gathering of host and guests at tea is called by that name and glosses it with the older Edo idiom 一世一度; the thought behind it is a sentence on the guest's conduct in the sixteenth-century tea record of Yamanoue Sōji 山上宗二.
We want you to be as happy with the meaning as you are with Master Takase's art. To learn more, visit Philology of 一期一会.