Many Latin verbs have entered English not from the infinitive but from the past passive participle: e.g., your fellate above is fello first person singular present indicative active, fellare infinitive, fellavi first person singular present perfect indicative active, fellatus past passive participle :- 'to suck'; its cousin irrumate from irrumo, irrumare, irrumavi, irrumatus :- 'to give the breast, give suck'. The four forms are lingo, lingere, linxi, linctus :- 'to lick'. So, I propose cunnilinct for the Englished verb. It may seem to be a tough form to get your tongue around but if you stick with it it'll seem natural enough in time.

Ceci n'est pas un seing.