Also, searching SE to find Applying/earning/validating leave and What does the "leave" mean in "parental leave" and "unpaid leave"? Answer The noun annual leave is uncountable. did not help.

The plural form of annual leave is also annual leave.

(29 of 30 words)

suggest that leave (absence from work) is a noun- uncountable, which means it has to be " leave " for plural.

Six weeks annual leave = six weeks holiday each year Leave of Absence = being allowed to be away from work Maternity Leave = permission given to woman to be away from work to give birth to a baby Sick Leave = period when a worker is away from work because of illness

Dictionaries (dictionary.com, OALD etc.) leave of absence| leaves of absence [plural] A period of time during which a person is absent from work or other duty for a reason other than normal holidays / vacation; may be paid or unpaid.