Double in magnitude, extent, or intensity.

Roget 35: increase, augment, add to, enlarge; dilate etc. (expand) 194; grow, wax, get ahead.    gain strength; advance; run up, shoot up; rise; ascend etc. 305; sprout etc. 194.    aggrandize; raise, exalt; deepen, heighten; strengthen; intensify, enhance, magnify, redouble; aggravate, exaggerate; exasperate, exacerbate; add fuel to the flame, oleum addere camino [Lat.], superadd etc. (add) 37; spread etc. (disperse) 73.    ... show more

Roget 90: double, redouble, duplicate, reduplicate; geminate; repeat etc. 104; renew etc. 660.   

Roget 104: repeat, iterate, reiterate, reproduce, echo, reecho, drum, harp upon, battologize^†, hammer, redouble.    recur, revert, return, reappear, recurse [Comp.]; renew etc. (restore) 660.    rehearse; do over again, say over again; ring the changes on; harp on the same string; din in the ear, drum in the ear; conjugate in all its moods tenses and conjugate in all its moods tenses and inflexions^†, begin again, go over the same ground, go the same round, never hear the last of; resume, return to, recapitulate, reword.    ... show more

Double again.

Make twice as great or intense.