When we use the phrase "allow in", it means to give permission for someone or something to enter a particular place. However, there are several synonyms that can be used instead of "allow in" to convey the same meaning. Some of the alternatives to "allow in" are let in, permit entry, grant access, give passage, and give the green light. Each of these phrases can be used in a variety of contexts, whether it's allowing someone to enter a building, granting access to a restricted area, or giving permission for a particular activity to happen. Choosing the right synonym depends on the situation and the level of formality required.