Frugal bath was running — little time to fill that (7)
I believe the answer is:
spartan
'frugal' is the definition.
(I've seen this before)
'bath was running little time to fill that' is the wordplay.
I cannot really understand how this works, but
'bath' could be 'spa' (Bath is a spa town) and 'spa' is found within the answer.
'time' could be 't' (abbreviation) and 't' is present in the answer.
The remaining letters 'ran' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for spartan that I've seen before include "Indifferent to luxury" , "Of conditions, simple and harsh as for ancient Greeks" , "Rather austere" , "austere old Greek" , "Austere, lacking comfort" .)