The question has come up again about both meaning and the identity (referent) of τὸ ἀρνίον τὸ ἐσφαγμένον in the Apocalypse. A discussion of which might be launched by looking at ὁ ἀμνὸς τοῦ θεοῦ in GJn 1:29,36.
John 1:29 Τῇ ἐπαύριον βλέπει τὸν Ἰησοῦν ἐρχόμενον πρὸς αὐτὸν καὶ λέγει· ἴδε ὁ ἀμνὸς τοῦ θεοῦ ὁ αἴρων τὴν ἁμαρτίαν τοῦ κόσμου.
John 1:36 καὶ ἐμβλέψας τῷ Ἰησοῦ περιπατοῦντι λέγει· ἴδε ὁ ἀμνὸς τοῦ θεοῦ.
Rev. 5:6 Καὶ εἶδον ἐν μέσῳ τοῦ θρόνου καὶ τῶν τεσσάρων ζῴων καὶ ἐν μέσῳ τῶν πρεσβυτέρων ἀρνίον ἑστηκὸς ὡς ἐσφαγμένον ἔχων κέρατα ἑπτὰ καὶ ὀφθαλμοὺς ἑπτὰ οἵ εἰσιν τὰ [ἑπτὰ] πνεύματα τοῦ θεοῦ ἀπεσταλμένοι εἰς πᾶσαν τὴν γῆν.
I would propose that John the Baptist used ἴδε ὁ ἀμνὸς τοῦ θεοῦ in primary reference to a apocalyptic ram who would literally remove τὴν ἁμαρτίαν from τοῦ κόσμου. That is he would not only atone for sin but actually eliminate sin from Kosmos.
The different words used in GJn and the Apocalypse are not sufficient grounds for demanding a different meaning or referent. First of all "little lambs" don't have seven horns. So I think we can discount the "diminutive" semantic component in τὸ ἀρνίον. Furthermore τὸ ἀρνίον wages war and inspires fear of his wrath. The blending of the sacrificial element with the warrior element is notable in both contexts. In other words, removing τὴν ἁμαρτίαν from τοῦ κόσμου might be though of as two themes woven together, sacrificial atonement and eschatological war.
There are other ways of reading the text. This is just a conjecture of mine which has been submitted for criticism in other forums over the last two decades. What I am trying to avoid is the either-or kind logic which demands the rejection of one theme if the other is accepted. John the Baptist was prophet. Prophets don't always understand all the ramifications of their message as they speak it. When he called Jesus ὁ ἀμνὸς τοῦ θεοῦ ὁ αἴρων τὴν ἁμαρτίαν τοῦ κόσμου, his notion of the message might have been predominately a divine warrior figure symbolized by an apocalyptic ram. In other words, like other prophets before him his words meant more than he knew at the time.