They're stern-looking in a row (7)
I believe the answer is:
oarsmen
'they're stern-looking in a' is the definition.
The definition suggests an adverb but the answer is not.
'row' is the wordplay.
I cannot really see how this works, but
'row' could be 'oar' (oar can mean to row with oars) and 'oar' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for oarsmen that I've seen before include "Crew - moaners (anag)" , "People in boats" , "They row boats" , "A sermon about rowers" , "They propel boats manually" .)