The phrase "alien to" refers to something that is unfamiliar, strange, or incompatible. There are several synonyms for this phrase such as foreign to, unknown to, unfamiliar to, unaccustomed to, apart from, different than, detached from, estranged from, removed from, and unconnected to. These synonyms convey a sense of distance, separation, or disassociation. For example, a new idea may be alien to some people because it is unfamiliar to them, while a person may feel estranged or removed from a community that is different than their own. Using these synonyms can help to convey a sense of otherness or contrast when describing a situation, idea, or experience.