tacit
TAS-itadjMeaning understood without being said out loud
Memory hook TAC = SILENT: a deal with no words. Across the dinner table, Zoe winks and Kai nods; without a word, they agree to swap peas for carrots. Their deal is tacit.
With a tacit nod, the twins agreed to keep the surprise party a secret.
In context No one ever announced the rule, but there was a tacit agreement in the house: whoever cooked dinner did not have to wash the dishes.
Similar unspoken, implied, understood, silent
Opposite explicit, stated, spoken
From Latin tacitus, “silent,” from tacere (to be silent). Taciturn comes from the same root.