U4, U-4, or U04 may refer to:
==Science and technology== U4 spliceosomal RNA, a non-coding RNA component of the major U2-dependent spliceosome Haplogroup U4 (mtDNA), a human genetic group U4, unitary group of degree 4 U-47700, a synthetic opioid U04, the ICD-10 code for severe acute respiratory syndrome
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).