Source : Webster's Revised Unabridged Dictionary (1913)

Proportionately \Pro*por"tion*ate*ly\, adv.
   In a proportionate manner; with due proportion;
   proportionally.

Source : WordNet®

proportionately
     adv 1: to a proportionate degree; "your salary will rise
            proportionately to your workload" [syn: {proportionally}]
            [ant: {disproportionately}]
     2: to a proportionate degree; "the height of this wall must be
        reduced proportionately to give the room pleasant
        dimensions" [ant: {disproportionately}]
     3: in proportion [syn: {pro rata}]