Bit of shelter by harbour (5)
I believe the answer is:
tenth
'bit' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe there's an association between them I don't understand?
'shelter by harbour' is the wordplay.
'shelter' becomes 'tent' (a tent is a kind of shelter).
'by' is a charade indicator (letters next to each other).
'harbour' becomes 'h' (this might be a standard abbreviation which I don't know about).
'tent'+'h'='TENTH'
'of' is the link.
Can you help me to learn more?
(Other definitions for tenth that I've seen before include "Ordinal number" , "Decimal part?" , "Fraction in tithe" , "0.1" , "Tithe proportion" .)