It takes money to feed one (5)
I believe the answer is:
meter
'feed one' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'it takes money to' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'takes' means one lot of letters goes inside another (take can mean to capture or invade).
'money' becomes 'm' (abbreviation used in economics).
'to' becomes 'eer' (I can't justify this - if you can you should believe this answer much more).
'm'+'eer'='meer'
't' placed inside 'meer' is 'METER'.
Can you help me to learn more?
(Other definitions for meter that I've seen before include "Instrument for measuring quantity" , "Device to measure quantity used of fluid, electricity etc" , "Gauge" , "Something measuring" , "Poe sometimes used this" .)