pecuniary (adj.) Look up pecuniary at Dictionary.com
c.1500, from Latin pecuniarius "pertaining to money," from pecunia "money, property, wealth," from pecu "cattle, flock," from PIE root *peku- "wealth, movable property, livestock" (source of Sanskrit pasu- "cattle," Gothic faihu "money, fortune," Old English feoh "cattle, money").

Livestock was the measure of wealth in the ancient world. For a possible parallel sense development in Old English, see fee, and compare, evolving in the other direction, cattle. Compare also Welsh tlws "jewel," cognate with Irish tlus "cattle," connected via notion of "valuable thing."