augment
verb (used with object)
to make larger; enlarge in size, number, strength, or extent; increase.
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
That was another source of dissatisfaction with King Angus of Gram; he had been augmenting his forces by hiring off-planet mercenaries.
From Space Viking by H. Beam Piper