The term "fellow-student" can be replaced with a plethora of other synonyms. Some options include "classmate," "peer," "colleague," "schoolmate," or "companion." Each synonym conveys a similar meaning but with a slightly different connotation. For instance, "classmate" implies that the individual is part of the same class, while "colleague" suggests a more professional relationship. "Schoolmate" emphasizes the shared experience of attending the same institution, while "companion" may imply a closer friendship. Ultimately, the choice of synonym depends on the context and the tone of the piece of writing.