Sentence:  Two millions were added to what had been set aside for it in Mrs. Meeker 's lifetime , and the proviso made that as long as Brian Thayer continued to discharge his duties as administrator of the fund to the satisfaction of the board of trustees ( hereinafter appointed by the bank administering the estate ) he was to be retained in his present capacity at a salary commensurate with the increased responsibilities <WSD>enlargement</WSD> of the fund would entail . 
Meaning of the word marked with <WSD> tags:  the act of increasing (something) in size or volume or quantity or scope