Again - Vine's Expository Dictionary of New Testament Words
Again[ 1,,G1364, dis ]
the ordinary numeral adverb signifying twice, is rendered again" in Philippians 4:16, "ye sent once and again unto my need," and in 1 Thessalonians 2:18, where Paul states that he would have come to the Thessalonians "once and again," that is, twice at least he had attempted to do so. See TWICE.
[ 2,,G3825, palin ]
the regular word for "again," is used chiefly in two senses,
(a) with reference to repeated action;
(b) rhetorically, in the sense of "moreover" or "further," indicating a statement to be added in the course of an argument, e.g., Matthew 5:33; or with the meaning "on the other hand, in turn," Luke 6:43; 1 Corinthians 12:21; 2 Corinthians 10:7; 1 John 2:8. In Hebrews 1:5 palin simply introduces an additional quotation; in Hebrews 1:6 this is not so. There the RV rightly puts the word "again" in connection with "He bringeth in the firstborn into the world," "When He again bringeth, etc." That is to say, palin is here set in contrast to the time when God first brought His Son into the world. This statement, then, refers to the future second advent of Christ. The word is used far more frequently in the Gospel of John than in any other book in the New Testament.
Note: Other words are rendered "again" in the AV, which the RV corrects, namely, deuteros and anothen. Deuteros signifies "a second time," John 9:24; Acts 11:9. Anothen signifies "from above, or anew." See the RV of John 3:3, John 3:7, and the AV and RV of John 3:31. Nicodemus was not puzzled about birth from Heaven; what perplexed him was that a person must be born a second time. This the context makes clear. This is really the meaning in Galatians 4:9, where it is associated with palin, "over again." The idea is "anew," for, though the bondage would be the same in essence and effect, it would be new in not being in bondage to idols but to the new Law. See also Matthew 27:51; Mark 15:38; John 19:23, "from the top." Anothen may mean "from the first," in Luke 1:3; Acts 26:5. For the meaning "from above," See James 1:17; James 3:15, James 3:17.