Likewise in syntactical lexica.
The headword is perhaps a future of e)ggumna/zw, which is used with the accusative of what is being exercised (body, soul, mind) and dative of the skill being practised. But the future middle participle appears as e)ggumnaso/menos with s-stem in Plato (see LSJ s.v.)
Alternatively [DW], the headword could be present tense of a compound e)ggumno/w.