Sino-Vietnamese word from 准 (“quasi-”) and 都督 (“admiral”). In Chinese, Japanese and Korean, 准 (zhǔn), meaning "quasi-" or "almost", is typically reserved for 准將 (zhǔnjiàng, “brigadier (general); (air) commodore”, literally “quasi-general officer”) and 准尉 (zhǔnwèi, “warrant officer”, literally “quasi-junior officer”), which is an additional fourth or fifth rank just below 少將 / 少将 (shàojiàng, “major general; rear admiral; air mashal”) or 少尉 (shàowèi, “first lieutenant; lieutenant junior grade; flying officer”). 准 (zhǔn) is thus outside the typical prefix scheme which includes 大 (highest), 上 ((second) highest), 中 (middle) and 少 (lowest). For the rank of "rear admiral", the prefix 少 would be more suitable (compare the army and air counterpart, thiếu tướng (“major general; air vice-marshal”)), but given Vietnamese's comparatively unorthodox and peculiar terminology, it is not used for this naval rank.
Vietnamese uses three specific terms for the three naval general officer ranks, namely đô đốc (“admiral”), phó đô đốc (“vice admiral”) and chuẩn đô đốc (“rear admiral”). In contrast, Chinese, Japanese and Korean use generic terms applicable in all branches, for example Japanese 大将 (taishō, “general; admiral; air chief marshal”), 中将 (chūjō, “lieutenant general; vice admiral; air mashal”) and 少将 (shōshō, “major general; vice admiral; air vice-marshal”); and lower ranks are generically termed, for example đại tá (“colonel; senior colonel; captain; commodore”).