Entries linking to selfsame
Old English self, sylf (West Saxon), seolf (Anglian), "one's own person, -self; own, personal; same, identical," from Proto-Germanic *selbaz (source also of Old Norse sjalfr, Old Frisian self, Dutch zelf, Old High German selb, German selb, selbst, Gothic silba), Proto-Germanic *selbaz "self," from PIE *sel-bho-, suffixed form of root *s(w)e-, pronoun of the third person and reflexive (referring back to the subject of a sentence), also used in forms denoting the speaker's social group, "(we our-)selves" (see idiom).
Its use as the second element in compounded reflexive pronouns (herself, etc.) was in Old English, from the original independent (and inflected) use of self following personal pronouns, as in ic selfa "myself," min selfes "of myself." With a merging of accusative, dative, and genitive cases.
As a noun from c. 1200 as "the person or thing previously specified;" early 14c. as "a person in relation to that same person." G.M. Hopkins used selve as a verb, "become or cause to become a unique self" (1880) but its use seems to have been restricted to poets.
"identical, equal; unchanging; one in substance or general character," from Proto-Germanic *samaz "same" (source also of Old Saxon, Old High German, Gothic sama, Old High German samant, German samt "together, with," Gothic samana "together," Dutch zamelen "to collect," German zusammen "together"), from PIE *samos "same," from suffixed form of root *sem- (1) "one; as one, together with."
Old English seems to have lost the adjective except in the adverbial phrase swa same "the same as" (literally "so same"). But the word that emerged in Middle English as "the ordinary adjectival pronominal designation of identity" [OED] is considered to be more likely (or mostly) from the Old Norse cognate same, samr "same." In its revival it replaced synonymous ilk.
As a pronoun, "the person or thing just mentioned," from c. 1300. In Middle English also a verb and an adjective, "together, mutually" (as in comen same "gather together, unite," kissen same "embrace one another").
Colloquial phrase same here "the same thing applies to me" as an exclamation of agreement is from 1895. All the same is from 1803 as "nevertheless, in spite of what has been mentioned." Same difference, a curious way to say "not different; equal," is attested from 1945. Often expanded for emphasis: ilk-same (mid-13c.); the self-same (early 15c.); one and the same is in Wyclif (late 14c.), translating Latin unus atque idem.