The English noun pound is from Latin pondō, short for lībra pondō, literally a pound (= lībra) by weight (= pondō)—Latin lībra denoted the Roman pound of twelve ounces, and pondō was a form of pondus, meaning weight.
In the sense of monetary unit, the noun pound originally denoted a pound weight of silver.
In the sense of unit of weight, pound is from a Germanic base derived from Latin pondō, meaning a pound weight, borrowed into Germanic at a very early date as a result of trade contacts and of the consequent necessity for accurate measurement.
In Latin, pondō was used with numerals as an indeclinable noun; for example, in Pro Aulo Cluentio Habito (For Aulus Cluentius Habitus), the Roman statesman, orator and author Marcus Tullius Cicero (106-43 BC) wrote:
auri¹ quinque pondo abstulit²
He took away five pounds of gold.
¹ auri, genitive of aurum, gold
² abstulit, 3rd person singular of the perfect tense of auferre, to take away
Latin pondō was short for lībra pondō, literally a pound by weight.
The Latin noun lībra denoted the Roman pound weight, of twelve ounces.
Both the conventional English signs lb., for pound(s) (in weight), and £ (earlier l.), for pound(s) (of money), are from lībra, which was used for pound in medieval Latin.
The Latin word was also used to denote a balance, pair of scales, hence to designate the constellation Libra, i.e. the Balance, or Scales.
An adverb meaning by weight, pondō was originally the ablative of an unattested form pondus, replaced by the noun pondus/ponder-, meaning a weight.
Derived from pondus/ponder-, the Latin verb ponderāre meant to weigh, and, figuratively, to weigh in the mind, to ponder, consider. The English verb ponder is from ponderāre via Middle French ponderer (Modern French pondérer).
The Latin noun pondus/ponder- was in turn derived from the verb pendĕre, meaning to weigh, literally to cause (the weighing scales) to hang down—from which was in turn derived the French verb pendre, to hang. The Latin verb was also used figuratively to mean to weigh mentally, to ponder, consider.
A frequentative form (i.e. a form expressing intensity of action) of pendĕre, the Latin verb pēnsāre meant to weigh out carefully, hence to ponder, consider. The French verb penser, to think, was derived from pēnsāre, and the English noun pansy is from French pensée, meaning heartsease, a transferred use of pensée, thought, the pansy being a symbol of remembrance.