The term 'ONE (VERY BEGINNING)' can be solved by the three letter word 'DAY'. The word 'DAY' is used to refer to a 24-hour period of time, usually measured from midnight to midnight. It is commonly used to refer to a specific DAY in a calendar, such as a particular date or holiday. In some contexts, it can also refer to a period of time that is shorter than a DAY, such as a workday or school DAY. In religious contexts, it can refer to a period of time that is longer than a DAY, such as a week or a month.