The Oxford Thesaurus An A-Z Dictionary of Synonyms - lag v.

1) fall behind, linger, loiter, delay, straggle, trail, hang back, dally, dawdle, inch or poke along: If you lag behind too far, you'll never catch up. 2) diminish, decrease, slacken, abate, slow (down or up) , flag, wane, ebb, falter, fail, let up, fall (off or away) , ease (up) , lighten: Contributions to the fund are lagging. Military preparations are lagging.