mid-15c., "plot where plants are raised from seeds," from Latin seminarium "plant nursery, seed plot," figuratively, "breeding ground," from seminarius "of seed," from semen (genitive seminis) "seed" (from PIE root *sē- "to sow"). Meaning "school for training priests" first recorded 1580s; commonly used for any school (especially academies for young ladies) from 1580s to 1930s.
variant of suffix -an (q.v.), with connective -i-. From Latin -ianus, in which the -i- originally was from the stem of the word being attached but later came to be felt as connective. In Middle English frequently it was -ien, via French.
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Harper, D. (n.d.). Etymology of seminarian. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/seminarian