diff --git a/src/main/java/com/ssu/unithon/sign/application/SignSentenceService.java b/src/main/java/com/ssu/unithon/sign/application/SignSentenceService.java
index e673938..fa31631 100644
--- a/src/main/java/com/ssu/unithon/sign/application/SignSentenceService.java
+++ b/src/main/java/com/ssu/unithon/sign/application/SignSentenceService.java
@@ -2,6 +2,7 @@
 
 import com.ssu.unithon.sign.infrastructure.openai.OpenAiClient;
 import java.util.List;
+import java.util.Set;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.stereotype.Service;
@@ -11,6 +12,11 @@ public class SignSentenceService {
 
     private static final Logger log = LoggerFactory.getLogger(SignSentenceService.class);
 
+    /** Standalone greetings/acknowledgements that don't need LLM composition — the single word already is the sentence. */
+    private static final Set<String> STANDALONE_WORDS = Set.of(
+        "감사합니다", "고맙습니다", "안녕하세요", "안녕", "네", "예", "아니요", "아니오"
+    );
+
     private static final String SYSTEM_PROMPT = """
         너는 실시간 접근성 통화 중계 서비스의 통역 보조 도구다. 통화 중 한쪽은 청각장애인(농인)이고, \
         그 사람은 한국수어로 상대방(비장애인)에게 무언가를 문의하거나 요청하는 중이다. \
@@ -46,6 +52,9 @@ public SignSentenceService(OpenAiClient client) {
 
     /** Converts a signed gloss sequence into one natural Korean sentence via an LLM, using prior turns as context, falling back to a plain join on failure. */
     public String compose(List<String> words, List<HistoryTurn> history) {
+        if (words.size() == 1 && STANDALONE_WORDS.contains(words.get(0).trim())) {
+            return words.get(0).trim();
+        }
         String joined = String.join(" ", words);
         String userMessage = buildUserMessage(words, history);
         try {
diff --git a/src/test/java/com/ssu/unithon/sign/api/SignControllerTests.java b/src/test/java/com/ssu/unithon/sign/api/SignControllerTests.java
index f299ae4..30d4ed7 100644
--- a/src/test/java/com/ssu/unithon/sign/api/SignControllerTests.java
+++ b/src/test/java/com/ssu/unithon/sign/api/SignControllerTests.java
@@ -80,6 +80,19 @@ void includes_history_in_the_prompt_when_provided() throws Exception {
             .contains("4시 변경");
     }
 
+    @Test
+    void returns_standalone_word_without_calling_the_llm() throws Exception {
+        String response = mvc.perform(post("/api/sign-language/compose")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"words\":[\"감사합니다\"]}"))
+            .andExpect(status().isOk())
+            .andReturn().getResponse().getContentAsString();
+
+        JsonNode body = json.readTree(response);
+        assertThat(body.get("sentence").asText()).isEqualTo("감사합니다");
+        assertThat(openAi.lastUserMessage).isNull();
+    }
+
     @Test
     void rejects_empty_word_list() throws Exception {
         mvc.perform(post("/api/sign-language/compose")