WordNet (r) 3.0 (2006):

let it go
    v 1: not act; "He thought of a reply but let it go"

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "let it go":
   abandon, allow for, bear with, blink at, brush aside, brush off,
   bury the hatchet, charge off, charge to experience, condone,
   connive at, dismiss, disregard, drop it, drop the subject, endure,
   forget, forget about it, forget it, forgive and forget, ignore,
   ignore it, lay aside, leave unavenged, let it pass, let slip,
   make allowances for, never mind, no matter, overlook, pass over,
   pocket the affront, push aside, put aside, regard with indulgence,
   set aside, shrug off, skip it, sneeze at, take, think nothing of,
   thrust aside, turn away from, wink at, write off