WordNet (r) 3.0 (2006):

at the same time
    adv 1: at the same instant; "they spoke simultaneously" [syn:
           simultaneously, at the same time]
    2: overlapping in duration; "concurrently with the conference an
       exhibition of things associated with Rutherford was held";
       "going to school and holding a job at the same time" [syn:
       concurrently, at the same time]

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "at the same time":
   above, ad interim, additionally, after all, again, albeit,
   all included, all the same, all together, also, although,
   altogether, among other things, and all, and also, and so,
   as far as, as long as, as one, as one man, as well, at a clip,
   at all events, at any rate, at one time, at that time,
   at which time, au reste, beside, besides, between acts,
   betweentimes, betweenwhiles, beyond, but, coinstantaneously,
   concurrently, contemporaneously, during the interval,
   during which time, else, en attendant, en plus, even, even so,
   extra, farther, for a time, for all that, for lagniappe,
   for the meantime, for the nonce, further, furthermore, howbeit,
   however, in a chorus, in addition, in any case, in any event,
   in chorus, in concert with, in phase, in sync, in the interim,
   in the meanwhile, in unison, inter alia, into the bargain,
   isochronously, item, just the same, likewise, meantime, meanwhile,
   more, moreover, nevertheless, nonetheless, notwithstanding,
   on that occasion, on the beat, on the side, on top of, over,
   pendente lite, plus, rather, similarly, simultaneously, still,
   synchronously, the while, then, therewith, though, to boot,
   together, too, until then, when, whereas, while, whilst,
   with one voice, yet