"\definefont[Test][file:your-font-file.otf]" should work, but I never used this approach.
I think you need to mix fonts into a typeface with something similar to a typescript (but this is all Greek to me).
Here’s an example of a simple typescript using "file": \definefontfeature[smallcaps][default][smcp=yes] \starttypescriptcollection[charis] \starttypescript [serif] [charis] \definefontsynonym [Charis-Roman] [file:CharisSIL-R.ttf] \definefontsynonym [Charis-Italic] [file:CharisSIL-I.ttf] \definefontsynonym [Charis-Bold] [file:CharisSIL-B.ttf] \definefontsynonym [Charis-BoldItalic] [file:CharisSIL-BI.ttf] \definefontsynonym [Charis-Roman-Caps] [Charis-Roman] \stoptypescript \starttypescript [serif] [charis] [name] \setups[font:fallback:serif] \definefontsynonym [Serif] [Charis-Roman][features=default] \definefontsynonym [SerifItalic] [Charis-Italic][features=default] \definefontsynonym [SerifBold] [Charis-Bold][features=default] \definefontsynonym [SerifBoldItalic] [Charis-BoldItalic][features=default] \definefontsynonym [SerifSlanted] [Charis-Italic][features=default] \definefontsynonym [SerifBoldSlanted] [Charis-BoldItalic][features=default] \definefontsynonym [SerifCaps] [Charis-Roman-Caps][features=smallcaps] \stoptypescript \starttypescript [charis] % doesn’t make a lot of sense \definetypeface [charis] [rm] [serif] [charis] [default] \definetypeface [charis] [ss] [sans] [heros] [default] \definetypeface [charis] [tt] [mono] [modern] [default] \definetypeface [charis] [mm] [math] [default] [default] \stoptypescript \stoptypescriptcollection Greetlings, Hraban --- https://www.fiee.net http://wiki.contextgarden.net https://www.dreiviertelhaus.de GPG Key ID 1C9B22FD