"You canker blossom!" 3 Shakespearean Insults
"craving, longing," 1796, perhaps a back-formation from lecher, or from a figurative use of latch (v.) in a secondary sense of "grasp, grasp on to."
: when Henry goes letching after Anne/ keep Junior from leching (1911+)
[fr lecher, lechery, ultimately fr the notion of licking]