Oscar meets Rod at sea, and they measure distance (9)
I believe the answer is:
odometers
'they measure distance' is the definition.
The definition suggests an adverb but the answer is not.
'oscar meets rod at sea' is the wordplay.
'oscar' becomes 'o' (phonetic alphabet: alpha, bravo, charlie etc.).
'at sea' is an anagram indicator.
'meets'+'rod'='meetsrod'
'meetsrod' anagrammed gives 'dometers'.
'o'+'dometers'='ODOMETERS'
'and' acts as a link.
Can you help me to learn more?
(Another definition for odometers that I've seen is " They show mileage in cars etc".)