moil

(verb) work hard. Synonyms: labor, labour, toil, fag, travail, grind, drudge, dig. Examples: "She was digging away at her math homework." "Lexicographers drudge all day long."

(verb) be agitated. Synonyms: churn, boil, roil. Example: "The sea was churning in the storm."

(verb) moisten or soil. Example: "Her tears moiled the letter."