An important SNOMED CT use case is to support semantic interoperability between electronic health records and aggregation terminologies such as ICD. From the ongoing alignment exercise between SNOMED CT and the new version of ICD, now in its pre-final form, we studied whether the ambiguity of clinical language as displayed by SNOMED CT synonyms hampers the quality of SNOMED CT axioms following the SNOMED CT “concept model”. We measure the rate of synonyms in the semantic misalignment between classes from the chapter on circulatory diseases of the ICD-11 beta version and SNOMED CT concepts with the same description names. Our study confirms that SNOMED CT synonyms are ambiguous and that there is a need to increase the number of SNOMED CT fully defined representations of Fully Specified Names (FSN), and of synonyms independently of their relations.