Third-person singular present tense; persuades someone not to do something they had planned or intended.
From Latin dissuadere (dis- 'away from' + suadere 'to urge, persuade'). The -s marks this as the present tense form for third-person singular (he/she/it dissuades).
Interestingly, 'dissuade' is rarer in modern English than you'd expect—most English speakers use 'talk out of' or 'persuade against' instead, showing how new vocabulary can displace older words.
Complete word intelligence in one call. Free tier — 50 lookups/day.