The word allay is an amalgamation of the dutch word, al, which means everyone or each, and the English word lay, which, until The Words Project gets to it, means to have sex with. That having been said, “everyone” is, admittedly, somewhat of an exaggeration.
Allay is, thus, an adjective that can have either of two meanings. When discussing a group of people, it suggests that promiscuity is widespread in that group. If, for example, a particular culture promotes free love and frequent, uninhibited casual sex, you could say that it is an allay culture.
When allay is used to describe an individual, it means that person is particularly promiscuous. For example, an allay man or woman is a man or woman who has sex with pretty well everyone he or she meets. (The sex of the people he or she beds is irrelevant to the use of the word allay.)