A Greek adjective/pronoun meaning another, other — specifically another of the same kind. This is contrasted with heteros (G2087), which means 'another of a different kind.' Though the distinction is not rigidly maintained in koinē Greek, it remains theologically significant in key passages.
The distinction between allos (same kind) and heteros (different kind) illuminates crucial theological truths. When Jesus promises 'another (allos) Helper' (John 14:16), He means the Spirit is the same kind of advocate as Jesus Himself — not a lesser substitute but an equal successor. When Paul warns that some preach 'a different (heteros) gospel' (Galatians 1:6), but immediately adds 'which is not another (allos)' — meaning there is no second legitimate gospel; what they preach is not just different, it's not even a gospel at all. This subtle word distinction preserves both the unity of the Trinity (Spirit = same kind as Son) and the exclusivity of the gospel (no alternative version exists).