Lacking energy, otter tries swimming to get a drink (9)

'a drink' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?

'lacking energy otter tries swimming' is the wordplay.
'lacking' suggests deleting specific letters.
'energy' becomes 'e' (physics symbol as in E=mc2).
'swimming' indicates an anagram.
'otter'+'tries'='ottertries'
'ottertries' with 'e' removed is 'ottrtries'.
'ottrtries' with letters rearranged gives 'RISTRETTO'.

'to get' acts as a link.

Can you help me to learn more?