"brutal initiation, act of abusing a newcomer," 1848, said to be a college word ("This word is used at Harvard College, to express the treatment which Freshmen sometimes receive from the higher classes, and especially from the Sophomores" -- "Collection of College Words and Customs," Boston, 1851), but perhaps originally nautical; see haze (v.).
The thing is older than the word. Compare pennalism "exceptional tyrannical hazing of college freshmen by older students at 17c. German Protestant universities," from German pennal (from Latin) "a pen-case;" also "a freshman," so called for the cases they dutifully carried to lectures.
1570s, "inferior in rank" (1540s as a noun, "junior pupil, freshman"), senses now obsolete, from French puisné (Modern French puîné), from Old French puisne "born later, younger, youngest" (12c., contrasted with aisné "first-born").
This is from puis nez, from puis "afterward" (from Vulgar Latin *postius, from Latin postea "after this, hereafter," from post "after," see post-, + ea "there") + Old French né "born," from Latin natus, past participle of nasci "be born" (Old Latin gnasci; from PIE root *gene- "give birth, beget"). Compare puisne.
The sense of "small, weak, insignificant, imperfectly developed in size or strength" is recorded from 1590s. Related: Puniness.