noun
long-term substitute teacher
Specifically a teacher filling in for someone on maternity leave, long-term sick leave, or similar extended absence. Not a short-term substitute.
産休の先生の代わりに、臨時的採用教員が来た。
A long-term substitute teacher came to replace the teacher on maternity leave.
非常勤講師 is a part-time lecturer or instructor, not necessarily a substitute. 臨時的採用教員 is specifically a temporary replacement for an absent regular teacher.
代用教員 is a more general term for a substitute teacher, which can be short-term. 臨時的採用教員 implies a longer, more formal temporary appointment.
Compound of 臨時的 (temporary, provisional) + 採用 (hiring, employment) + 教員 (teacher, instructor).