What does the cryptic crossword clue "Lay out pound in old coins (5)" mean?

The definition part of the clue is "Lay". The answer is SPEND. Explanation: PEN [pound] in S [shillings] D [pence] – old coins

Lay out pound in old coins (5)

Guardian Puzzle #27821 22 Down 2019-05-15

Definition

Lay

Explanation

PEN [pound] in S [shillings] D [pence] – old coins

Source: Fifteensquared

Answer

SPEND