It may run on gas (or after a taxi?) (5)
I believe the answer is:
meter
'it may run on gas or after a taxi?' is the definition.
The definition suggests a singular noun which matches the answer.
'it may run on' is the wordplay.
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'may' becomes 'met' (I can't explain this - if you can you should believe this answer much more).
'run' becomes 'r' (cricket abbreviation).
'on' is an insertion indicator (as in clothing \'on\' a person).
'met'+'r'='metr'
'e' inserted inside 'metr' is 'METER'.
Can you help me to learn more?
(Other definitions for meter that I've seen before include "Instrument for measuring quantity" , "Device for measuring and recording" , "Device to measure quantity used of fluid, electricity etc" , "Measuring device as for electricity usage (5)" , "Measuring device, say for electricity usage" .)