Wityh this working example:

\starttext
The quick brown fox jumped over the lazy dog

\definefontfeature
[effect-widen]
  [effect={width=.2,delta=0.3}]
\definedfont[Sans*widen,effect-widen]
The quick brown fox jumped over the lazy dog

\stoptext

I am puzzling to turn my working \definedfont into a \definefont so I can use that instead.

Actually, my setup is Optima with Helvetica used for Cyrillic:

\definefallbackfamily
  [archimate]
  [ss]
  [Helvetica]
  [preset=range:cyrillic,
   tf=style:light,
   it=style:lightoblique,
   bf=style:regular,
   bi=style:oblique,
   force=yes,
   rscale=1.0]
\definefontfamily [archimate] [ss] [Optima]
\setupbodyfont[archimate]

And I would like the effect to work on just the Optima font (which is a bit light for this use)

I’ve been trying to work out using \definefont with the effect but have so far failed.

Thanks,

G