Slovenly nature of old nurse drinking coffee at bar on ship (14)

'slovenly nature' is the definition.
(slatternly means slovenly or untidy)

'old nurse drinking coffee at bar on ship' is the wordplay.
I cannot really understand how this works, but
'nurse' could be 'rn' (RN is an example) and 'rn' is found within the answer.
'coffee' could be 'latte' (I've seen this before) and 'latte' is present in the answer.
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is found in the answer.
'bar' could be 'less' (both can mean 'not including') and 'less' is located in the remaining letters.
A single letter 's' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

'of' acts as a link.

Can you help me to learn more?