Online PhD application systems usually ask for relation between the recommender and the applicant.
The applicant was in a PhD program and the recommender was a professor in the department. The applicant approached him for some research opportunities at first, and later did some research in one of the recommender's projects, directly mentored by an assistant research professor. There was no formal title of "research adviser" for the recommender to the applicant, or for the research assistant professor to the applicant, as the student was still in the process of finalizing research direction and adviser. The student then didn't finish the PhD, and later applied to PhD programs in other universities.
Can the relation between the recommender and the applicant be "research adviser" in PhD application? What is best to describe that relation? By the way, the recommender was also an instructor to the applicant in some courses. But a relation besides "instructor" was preferred, if possible.