Experimental Factor Ontology
Application ontology for experimental variables. Combines parts of ontologies to describe experimental designs.
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Where this one tends to earn its keep.
GWAS Catalog trait annotation
Expression Atlas condition annotation
Biobank sample metadata
Clinical trial variable classification
I haven't checked this label against the actual licence text — it's the catalogue's original guess. Check the ontology's own site before you rely on it.
Others worth a look in Life Sciences.